Cho phương trình 3x2 + 7x + 4 = 0.

Xác định các hệ số a, b, c rồi tính a - b + c.

Khi hiđro hóa hoàn toàn chất X (C₅H₈) thu được isopentan. Vậy công thức cấu tạo có thể có của X là?

A. 1 và 2

B. 2 và 3

C. 1 và 4

D. Tất cả đều thỏa mãn

Read the following passage carefully and then choose the best option to fit each space. Identify your choice by circling letter A, B, C or D on the answer sheet.

          The 18^th-century battlefield was, compared with that of the 20^`th-century, an intimate theatre, especially intimate in the (19)___ of the Revolution, which was usually small even by the standards of the day. Soldiers had to come to close quarters to kill; this fact reduced the mystery of the battle, though perhaps not its terrors. But at least the battle field lost some of its impersonality. In fact, in (20)___  to (with) the 20^1h-century combat, in which the enemy usually remains unseen and the source of incoming fire unknown, in the 18^1h-century battles the enemy could be seen and sometimes even (21)___ . (22)____ one's enemy may have arose a singular (23) ____of feeling uncommon in modern battles. Before the (24)___ occurred tension and anxiety (25) _____ up as the troops marched from their column into a line of attack. The ( 26) ____ of their movements was well understood by themselves and their enemies, who must have watched with feeling of dread and fascination. When the order came sending them (27) ____ rages, even madness replaced the attacker's (28) ____, while terror and desperation filled those who received  the charge.

Điền vào số (24)

A. assault             

B. confrontation    

C. obedience  

D. order

They wanted ______ if anything happened.

A. to be told

B. to tell 

C. Telling

D. being told

It turned out that we………….rushed to the airport as the plane was delayed by several hours

A. can’t  have

B. should have

C. may have

D. needn’t have

Mark the letter A, B, C or D on your answer sheet to indicate the sentence that is closest in meaning to each of the following questions.

I'm sure Mary was very disappointed when she failed to get the scholarship.

A. Mary may be very disappointed when she failed to get the scholarship.

B. Mary could have been very disappointed when she failed to get the scholarship.

C. Mary must have been very disappointed when she failed to get the scholarship.

D. Mary must be very disappointed when she failed to get the scholarship.

Cho 29,8 gam hỗn hợp 2 amin no đơn chức kế tiếp tác dụng hết với dung dịch HCl, làm khô dung dịch thu được 51,7 gam muối khan. Công thức phân tử 2 amin là

A. C₂H₅N và C₃H₇N

B. C₂H₇N và C₃H₉N

C. CH₅N và C₂H₇N.

D. C₃H₉N và C₄H₁₁N