问题

It’s said that this kind of plant only gives off this strange perfume on ________ conditions which the scientists are trying to figure out now.

A:outstanding
B:certain
C:obvious
D:ordinary

正确答案是：

同类题型

explained on the phone, your request will be considered at the next meeting.

___we have satisfied you, you have no grounds of complaint

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__ _______ mon whether you put your heartinto it．