1 At one time we had about eighty people here who did nothin

1选D
解析：but做介词(except的用法也基本相同),有时后接带to的动词不定式,有时后接不带to的动词不定式.
当句子中有do时,but后面跟的动词不定式通常不用to,其基本结构是：
do nothing (anything) but do……；have……to do but do.否则,不定式符号to不能省略.如：
The enemy could do nothing but surrender.
敌人毫无办法,只得投降.
There is nothing left to him but to hit back.
他只能回击,别无他法.
除了什么只能做什么.
I can do nothing but do the homework.
无可选择不得不做什么.
He had no choice but to join the party.
除了做什么没事可做.
She had nothing to do but go on working
2选B
当有人敲门,你不知道此人是谁或者不知道他是男性还是女性,此时可用it来指代此人.故选B
3选C
后面的句子是主句,前面的那个句子是从句.主句主语是the meeting,而从句不是.故ABD放进去后nobody变成了主语,一个句子不能有2个不同的主语.所以选C.
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