问题描述：
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.
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.
问题解答：
我来补答展开全文阅读