Cho phương trình m + sin m + sin 3 x = sin 3 sin x + 4 sin 3 x .  Có bao nhiêu số nguyên m để phương trình có nghiệm thực?

A. 4

B. 5

C. 8

D. 9

Loại polime nào sau đây được điều chế bằng phản ứng trùng ngưng?

A. Polietilen

B. Nhựa phenolfomanđehit

C. Tơ nitron

D. Poli(vinyl clorua)

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct word or phrases that best fits each of the numbered blanks.

Why is it that many teenagers have the energy to play computer games until late at night but can’t find the energy to get out of bed (39) _________ for school? According to a new report, today’s generation of children are in danger of getting so (40) _________ sleep that they are putting their mental and physical health at (41) _________ . Adults can easily survive on seven to eight hours’ sleep a night, (42) _________ teenagers require nine or ten hours. According to medical experts, one in five youngsters (43) _________ anything between two and five hours’ sleep a night less than their parents did at their age

Điền ô số 40

A. few

B. less

C. much

D. little