选择题：______when to start out,he went to ask his captain

选择题：______when to start out,he went to ask his captain
when to start out,he went to ask his captain
1.Not to know 2,Don't know 3,Not knowing 4,Not known
主要请解释这句话的结构!

选3
首先这个句子真正的谓语是went,因此第二个谓语动词要用非谓语动词.因此排除2
不定式和分词作状语的区别
1. 现在分词与过去分词作状语的区别.
现在分词（v-ing）与过去分词（V-ed或不规则）做状语的最主要区别在于
两者与所修饰的主语的主动与被动关系的区别.
1）现在分词作状语时,现在分词的动作就是句子主语的动作,它们之间的关系是主动关系.
He went out shutting the door behind him.
他出去后将门随手关上.
Not knowing what to do, he went to his parents for help. （同本题）
由于不知如何办是好,他去找父母帮忙.
2）过去分词作状语时,过去分词表示的动作是句子主语承受的动作,它们之间的关系是被动关系.
Given more attention, the trees could have grown better.
如果对这些树多关心一些,它们本来会长得更好.
Faced with difficulties, we must try to overcome them.
在遇到困难的时候,我们必须设法克服.
2 动词不定式和分词作状语的区别
1)分词作状语一般表示伴随,而不定式常常表示目的.
They stood by the roadside talking about the plan．他们站在路边谈论着这个计划.(伴随)
They stood by the roadside to talk about the plan．他们站在路边为的是谈论这个计划.(目的)
2)分词作状语放在句子开头,除表示原因之外有时表示时间或条件.动词不定式作状语时,除了表示目的以外,还表示结果或原因.
Reading attentively,he forgot the time for lunch．
由于在专心读书,他忘了吃午饭的时间.(原因)
Reading carefully,he found something he had not known before．
他仔细读书时,发现了一些从前不知道的东西.(时间)
Reading carefully,you'll learn something new．
只要你仔细阅读,你会学到一些新的东西.(条件)
His family was too poor to support him．他的家庭太穷,不能维持他的生活.(结果)
The boy is not tall enough to reach the book shelf．这男孩个子不够高,手伸不到书架.(结果)
We are glad to hear the news．我们很高兴听到这消息.(原因)
To see him behaved in that way , I would think that he must have got something wrong with himself . 看到他这样的行为,我想他肯定有点不对劲.（注意时间上的不同）
根据上边的分析,你在对号入座,首先,本句话的主语是he,因为是他不知道,因此肯定是主动的排除4,排除1是因为时间不对,不定式是指将要发生的.
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