21. When a giraffe has ______ drink, it has to stand with its front legs wide apart in order to reach ______ water easily.
A. 不填；不填 B. a; the C. the; 不填 D. 不填；the
22. ----Haven't seen you for ages! Do you still work in Xi'an?
----________. It's four years since I worked there.
A. No, I don't. B. No, I haven't. C. Yes, I do. D. Yes, I have
23. He wondered ________ his son was getting along with the experiment.
A. when B. what C. how D. which
