21. — Sally, our monitor, was late for her class this morning.
— ______? As far as I know, she never came late to class.
A. How come B. What for C. So what D. Why not
22. We don’t think the experiment is ___ failure. At least we have gained ___ experience for future success.
A. the; a B. a; / C. a; an D. the; the
