问题

It is believed to _____ over by sandstorms from AD 200 to AD 400.
A:gradually cover
B:be gradually being covered
C:have been gradually covered
D:be gradually covered;
B:be gradually being covered
C:have been gradually covered
D:be gradually covered;
正确答案是:
同类题型
Father won’t allow me to play outside ________ I wash up the dishes.
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The teacher was surprised to see lots of people_____at the back of the room_____worried. [ ]
I don’t care how my parents think of me .– Well , in fact I think you __________ .