Cho hình vẽ mô tả thí nghiệm pha dung dịch axit X loãng bằng rót từ từ dung dịch axit đặc vào nước :

Hình vẽ trên minh họa nguyên tắc pha chế axit nào sau đây?

A. HCl.

B. H₂SO₄.

C. HNO₃.

D. H₃PO₄.

Phát biểu nào sau đây đúng?

A. Tơ visco, tơ xenlulozơ axetat thuộc loại tơ tổng hợp

B. Sợi bông, tơ tằm là polime thiên nhiên

C. Polietilen và poli(vinyl clorua) là sản phẩm của phản ứng trùng ngưng

D. Tơ nilon-6,6 được điều chế từ hexametylenđiamin và axit axetic

Cho m gam Mg vào dung dịch X gồm 0,03 mol Zn(NO₃)₂ và 0,05 mol Cu(NO₃)₂ , sau một thòi gian thu được 5,25 gam kim loại và dung dịch Y. Cho dung dịch NaOH vào Y, khối lượng kết tủa lớn nhất thu được là 6,67 gam. Giá trị của m là

A. 3,60

B. 2,02

C. 4,05

D. 2,86.

Thực hiện phép lai P: ♂ AaBbCcDdee x ♀ aaBbCCDdEE. Theo lý thuyết, tỉ lệ cá thể mang kiểu hình khác với bố và mẹ ở F1 là bao nhiêu ? Biết một gen quy định một tính trạng, trội lặn hoàn toàn

A. 31,25%

B.25%

C.71,875%

D.50%

Mark the letter A, B, C, or D on your answer sheet to indicate the word(s) CLOSEST in meaning to the

underlined word(s) in each of the following questions.

The museum was overrun with tourists, so I decided to go back another city.

A. having no tourists

B. not having enough tourists

C. crowded with tourists 

D. having tourists running

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 38 to 42.

(1) Though Edmund Halley was most famous because of his achievements as an astronomer, he was a scientist of diverse interests and great skill. In addition to studying the skies, Halley was also deeply interested in exploring the unknown depths of the oceans. One of his lesser-known accomplishments that were quite remarkable was his design for a diving bell that facilitated exploration of the watery depths.

(2) The diving bell that Halley designed had a major advantage over the diving bells that were in use prior to his. Earlier diving bells could only make use of the air contained within the bell itself, so divers had to surface when the air inside the bell ran low. Halley’s bell was an improvement in that its design allowed for an additional supply of fresh air that enabled a crew of divers to remain underwater for several hours.

(3) The diving contraption that Halley designed was in the shape of a bell that measured three feet across the top and five feet across the bottom and could hold several divers comfortably; it was open at the bottom so that divers could swim in and out at will. The bell was built of wood, which was first heavily tarred to make it water repellent and was then covered with a half-ton sheet of lead to make the bell heavy enough to sink in water. The bell shape held air inside for the divers to breathe as the bell sank to the bottom.

(4) The air inside the bell was not the only source of air for the divers to breathe, and it was this improvement that made Halley’s bell superior to its predecessors. In addition to the air already in the bell, air was also supplied to the divers from a lead barrel that was lowered to the ocean floor close to the bell itself. Air flowed through a leather pipe from the lead barrel on the ocean floor to the bell. The diver could breathe the air from a position inside the bell, or he could move around outside the bell wearing a diving suit that consisted of a lead bell-shaped helmet with a glass viewing window and a leather body suit, with a leather pipe carrying fresh air from the diving bell to the helmet. 

The subject of the preceding passage was most likely Halley’s _____.

A. childhood

B. work as an astronomer

C. invention of the diving bell

D. many different interests

Cho X, Y, Z, T là các chất khác nhau trong số 4 chất: CH_­3­NH_­2, ­NH_­3­, C₆H₅­OH (phenol), C₆­H_­5­NH_­2­ (anilin) và các tính chất được ghi trong bảng sau:

Nhận xét nào sau đây không đúng?

A. ­Dung dịch X có tính axit; dung dịch Y, Z, T có tính bazơ

B. X, Y tạo kết tủa trắng với nước brom

C. Phân biệt dung X với dung dịch­ Y bằng quỳ tím

D. ­Z, T làm xanh quỳ tím ẩm

Read the following passage and mark the letter A, B, C or D to indicate the correct answer to each of the questions from 43 to 50.

It is estimated that over 99 percent of all species that ever existed have become extinct. What causes extinction? When a species is no longer adapted to a changed environment, it may perish. The exact causes of a species' death vary from situation to situation. Rapid ecological change may render an environment hostile to a species. For example, temperatures may change and a species may not be adapted. Food resources may be affected by environmental changes, which will then cause problems for a species requiring these resources. Other species may become better adapted to an environment, resulting in competition and, ultimately, in the death of a species.

The fossil record reveals that extinction has occurred throughout the history of Earth. Recent analyses have also revealed that on some occasions many species became extinct at the same time - a mass extinction. One of the best-known examples of mass extinction occurred 65 million years ago with the demise of dinosaurs and many other forms of life. Perhaps the largest mass extinction was the one that occurred 225 million years ago, when approximately 95 percent of all species died. Mass extinctions can be caused by a relatively rapid change in the environment and can be worsened by the close interrelationship of many species. If, for example, something were to happen to destroy much of the plankton in the oceans, then the oxygen content of Earth would drop, even affect organisms not living in the oceans. Such a change would probably lead to a mass extinction.

One interesting, and controversial, finding is that extinctions during the past 250 million years have tended to be more intense every 26 million years. The periodic extinction might be due to intersection of the earth's orbit with a cloud of comets, but this theory is purely speculative. Some researchers have also speculated that extinction may often be random. That is, certain species may be eliminated and others may survive for no particular reason. A species' survival may have nothing to do with its ability or inability to adapt. If so, some of revolutionary history may reflect a sequence of essentially random events.

Question 48: According to paragraph 2, evidence from fossils suggests that

A. extinctions on Earth have generally been massive

B. dinosaurs became extinct much earlier than scientists originally believed

C. there has been only one mass extinction in Earth's history

D. extinction of species has occurred from time to time throughout Earth's history