Theo em những nguyên nhân nào khiến cho Lê- ô-nác-đô đa Vin-xi trở thành họa sĩ nổi tiếng? Nguyên nhân nào là quan trọng nhất?

Hòa tan hoàn toàn 100 gam hỗn hợp X gồm Fe, Cu , Ag trong dung dịch HNO 3 (dư). Kết thúc phản ứng thu được 13,44 lít hỗn hợp khí Y gồm NO 2 , NO, N 2 O theo tỉ lệ số mol tương ứng là 3 : 2 : 1 và dung dịch Z (không chứa muối NH 4 NO 3 ). Cô cạn dung dịch Z thu được m gam muối khan. Giá trị của m và số mol HNO 3  đã phản ứng lần lượt là: 

A. 205,4 gam và 2,5 mol 

B. 199,2 gam và 2,4 mol 

C. 205,4 gam và 2,4 mol 

D. 199,2 gam và 2,5 mol 

Cho phản ứng hạt nhân 17 37 C l + Z A X → n + 18 37 A r .  Trong đó hạt X có

A. Z = 1; A = 3

B. Z = 2; A = 4

C. Z = 2; A = 3

D. Z = 1; A = 1

Lập bảng biến thiên và vẽ đồ thị của các hàm số: y = -x2 + 3x + 2

Kim loại nào sau đây là kim loại kiềm thổ?

A. K. 

B. Ba.         

C. Al.          

D. Zn.

Cho phản ứng: 

F e x O y + H N O 3 → F e N O 3 3 + N a O b + H 2 O

Hệ số của Fe(NO₃)₃ sau khi cân bằng 

Diễn thế thứ sinh có đặc điểm nào sau đây?

A. Bắt đầu từ một môi trường chưa có sinh vật

B. Được biến đổi tuần tự qua các quần xã trung gian

C. Quá trình diễn thế luôn gắn liền với sự phá hại môi trường

D. Kết quả cuối cùng luôn dẫn tới hình thành quần xã đỉnh cực

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 question.

        Most people start smoking when they are in their teens and are addicted by the time they reach adulthood. Some have tried to quit but have returned to cigarettes because smoking is such a strong addiction. It is a habit that is very difficult to break. There are many different reasons why people smoke.

        Three of the main reasons that young people smoke are to look mature, to be like their friends, and to experiment. Since teens see older people all around them smoking, especially their parents and relatives, they smoke to act older. If their friends or peers smoke, they may feel pressured into doing the same to be accepted. The last reason is the excitement of experimenting with something that is forbidden. In Massachusetts it is against the law for anyone under 18 years old to smoke. Usually parents do not allow their under age teens to smoke. Therefore, smoking becomes very attractive. It is exciting to get cigarettes and sneak away to smoke without being caught.

         Adults smoke for other reasons. They may have a lot of stress and pressures because of economic and personal problems. They may be unemployed or working but not making enough money to take care of themselves and their families. They may be homeless, or they may be dealing with alcohol or cocaine/heroin addictions. Some may be in bad marriages or relationships in which there is physical and/or verbal abuse. All these people may smoke to feel relaxed or to give them energy while going through a hard time.

        Whether young or old, some people smoke to control their weight. Smokers, on the average, weigh seven pounds less than non-smokers. Smoking reduces a person's appetite. It lessens his/her sense of taste and smell. This could be why ex-smokers gain weight after quitting cigarettes. Food tastes and smells so much better.

        Finally, there are people who say they love to smoke. Smoking gives them pleasure. It just makes them feel good.

What is the purpose of the whole passage?

A. To contrast young and old smokers.

B. To explain why people start smoking.

C. To demonstrate the attraction of cigarettes among the young.

D. To show the similarities between young and old smokers.

Mark the letter A, B, C or D on your answer sheet to indicate the word(s) CLOSET in meaning to the underlined word(s) in each of the following questions.

She lost her temper with a customer and shouted at him.

A. became very angry

B. kept her temper

C. had a temperature

D. felt worried

Rivers are on of the world's most important natural resources. Many cities are on the large rivers, and (1).................................. every country has a least one river that (2)................................... an important part in the lives of its people. Besides transportation, rivers (3)....................................... water for crops, water to drink, and recreation for people who live along their (4)......................................... And in (5)................................ to get water for crops, engineers sometimes build a dam (6).................................... a river and let water become a lake behind the dam. Then people can use their water not (7).................................... to irrigate fields but also to make electricity for homes and industries. (8)....................................... the water often becomes polluted when cities on river bank grow (9)....................................... and the number of industries increases. We are learning that it is necessary to (10)........................................ rivers clean if we want to enjoy the benefits of the natural resources.