21. You will surely get access ______ the internet; it’s only _____ matter of time.
A. of; a B. to; a C. on; the D. to; the
23. I found Mary _______ at the desk, ________ her homework carefully.
A. sitting; do B. sit; doing C. seated; do D. seated; doing
25. I can hardly believe it is a big family ________ twenty people.
A. consists of B. make up of C. consisting of D. making up of
请解释一下,谢谢