We did nothing but sit in the chair中 but后为什么接动词原形

注意but的第三种用法：
but的用法--"排除式"
but是"除了……以外"的意思,相当于except。
(1)but后也可以接名词或代词作宾语。例如:
1. They all went to the park ________ Mike and me.
A. besides B. except for C. but D. beside
析:Key: C。因为all是信息词,且they与Mike and me是"同类项",根据句意应选C。
(2)but常与下列词连用:a.否定词no one, none, nothing等; b.疑问词who, what等; c.不定代词all, everyone等。例如:
1. Nothing but disaster would come from such a plan.这个计划只能招灾惹祸,别无益处。
2. Who but Tom would do such a thing?除了汤姆以外还有谁愿意干这种事?
(3)but后可接动词不定式。注意:当but前面有实义动词do以及其相应形式作谓语动词时,则其后跟不带"to"的动词不定式,反之加"to"。例如:
1. David could do nothing but ________ his teacher yesterday afternoon.
A. help B. helped
C. helping D. to help
析:key:A。do nothing but...后应接动词原形,意为"除做……外什么也不做"。
2. The enemy had no choice but ________ their arms and ________ .
A. lie down;give in
B. lay down;give in
C. to lay down;give in
D. to lie down;to give in
析:Key:C。have no choice but后应接带to 的动词不定式,且and后的成分与动词不定式之间存在并列关系,故选C。
注意:but for是"要不是;没有……"的意思,常用于虚拟语气。例如:
But for your help, I would have failed. 要是没有你的帮助, 我早就失败了。
此外：apart from也可表示此意，其用法相当与besides, except for
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do nothing but do
n.只,仅
这是习惯用法.
我们只有坐在椅子上.