2^2a +2^2b không là chính phương với mọi số nguyên dương a;b

Read the following passage and mark the letter A, B, C or B on your answer sheet to indicate the correct answer to each of the questions from 30 to 37.

  These days, most people in Britain and the US do not wear veiy 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 are in a foreign country, the best way the writer suggests to you is to wear

A. strange clothes

B. as the people there do

C. your native clothes 

D. comfortable clothes

Mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questions.

What beautiful eyes..................!

A. does she have

B. she has

C. has she

D. she doesn't have

Thủy phân hoàn toàn a gam este đơn chức X được 3,2 gam CH₃OH và 0,7666a gam axit cacboxylic. Xác định CTCT của X, cho rằng X thực hiện phản ứng thủy phân ( R là C_xH_y hoặc H) như sau:

R−COO-CH₃ + H₂O →  R – COOH + CH₃− OH