21.So far nobody has provided ______ hard evidence to support their claim that they have seen _______ UFO.
A. an; a B. the; the C. 不填；a D. 不填；an
22. The foreign guests spoke highly of the children and their shows ___________ they saw in the kindergarten.
A. what B. who C. that D. which
23. I’ve had enough of my boss. He is rather too hard ___________ me.
A. for B. at C. on D. in
