Phép tính 1 x + 1 + 1 1 − x + 2x 2 x 2 − 1  có kết quả là?

A.  x 2 + 2x (x − 1)(x + 1)

B. 2

C.  2x 2 + 2 (x − 1)(x + 1)

D.  2x 2 x 2 − 1

Choose the best answer

He spends most of his time ____________charity work.

A. with doing

B. did

C. doing

D. to do