为什么这里要用by doing?在这里,How would you account for the fact that explorers used to be willing to take great risks,by sailing across the sea without navigational instruments?by sailing.在这里的用法我不是很理解.

为什么这里要用by doing?在这里,How would you account for the fact that explorers used to be willing to take great risks,by sailing across the sea without navigational instruments?by sailing.在这里的用法我不是很理解. but There is no excuse for not doing your homework 这里do为什么要用doing 吉姆已经做完作业了：Jim has finished doing his housework.这里为什么要用doing what's the time ()your watch 为什么要用介词by by在这里的中文意思是什么? what is she doing这里为什么用is? it is more adj.to do than to do 在这里为什么不可以用doing?在这里为什么不可以用doing?我觉得这个to do是逻辑主语,又是泛指,应用doing呀 by 在这里的含义及用法Existing reserves of fossil fuel by will have run out 2045这个句子里by的含义及用法,这里为什么要用倒装呢？ Reading books is better than sitting there without doing anying.请问这里为什么要用sitting? consider+doing?这里为什么to do It is a waste of time doing this这里为什么用doing而不用do?为什么? what dose she mean by'change'in the last sentence?mean是什么意思?为什么要用by,在这里起什么作用 before the closing of the store为什么这里要用closing?closing 在这里是什么词性? I have just arrived by train这里为什么要用现在完成时呢 请问语法结构 by doing A and do B 还是 by doing A and doing 这里是并列结构对么?` 介词用法he is junior to me by two years.这里为什么用by?这里是什么用法? 请问What is the time by your watch?这里为什么要用by呢选项中有ON pay attention to doing为什么to在这里是介词而不是连词? 你为什么在这里用英语怎么说