(   ) 16. Personal computers were in              use in China when Amy visited the country in       twentieth century(ÊÀ¼Í).

A. the, /       B. the, the        C. / , /          D. /, the

(   ) 17. The magic show has been on       20 minutes. It has been on        2.p.m..

A. for, since    B. in, since       C. for, for       D. since, for

(    ) 18. – Where is your mother?

- She together with her friends           Shanghai.

A. has gone to   B. have gone to    C. has been to    D. have been to