Cho hình chóp S.ABCD có đáy là hình vuông cạnh a, tam giác SAB đều và nằm trong mặt phẳng vuông góc với đáy. Tính khoảng cách giữa hai đường thẳng chéo nhau SA và BC.

A.  a 3 2

B. a

C.  a 3 4

D.  a 2  

Mark the letter A, B, C, or D on your answer sheet to indicate the sentence that best combines each pair of sentences in the following questions.

Mr. Hung is a professor. His car was stolen yesterday.

A. His car was stolen yesterday, Mr Hung is a professor

B. Mr. Hung, who his car was stolen yesterday, is a professor

C. Mr. Hung, who is a professor, his car was stolen yesterday

D. Mr. Hung, whose car was stolen yesterday, is a professor