Xác định giá trị của tham số m để hàm số y = x 3  + m x 2  - 3 có cực đại và cực tiểu.

A. m = 3;              B. m > 0;

C. m ≠ 0;              D. m < 0.

Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the correct answer to each question.

These days, most people in Britain and the US do not wear very formal clothes. But sometimes it is important to wear the right thing.

Many British people don't think about clothes very much. They just like to be comfortable. When they go out to enjoy themselves, they can wear almost anything. At theatres, cinemas and concerts you can put on what you like from elegant suits and dresses to jeans and sweaters. Anything goes, as long as you look clean and tidy.

But in Britain, as well as in the US, men in offices usually wear suits and ties, and women wear dresses or skirts (not trousers). Doctors, lawyers and business people wear quite formal clothes. And in some hotels and restaurants men have to wear ties and women wear smart dresses.

In many years, Americans are more relaxed than British people, but they are more careful with their clothes. At home, or on holiday, most Americans wear informal or sporty clothes. But when they go out in the evening, they like to look elegant. In good hotels and restaurants, men have to wear jackets and ties, and women wear pretty clothes and smart hairstyles.

It is difficult to say exactly what people wear informal or formal in Britain and the US, because everyone is different. If you are not sure what to wear, watch what other people do and then do the same. You'll feel more relaxed if you don't look too different from everyone else.

If you visit an American friend at home in the evening, you may find that your friend wears

A. pretty clothes

B. formal clothes

C. dirty clothes

D. informal clothes