Hãy vẽ mũi tên chỉ chuyển động của phần tử M khi sóng truyền từ trái sang phải (H.7.4 SGK).

Mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questions.
It was a serious operation but he made a complete recovery and was soon as fit as a fiddle.

A. in careful health

B. in easy health

C. in quiet health

D. in good health

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

Now I _____________ Havard University.

A. am attending

B. attend 

C. was attending 

D. attended