请问一下at the age of 与 by the age of 的区别.
问题描述：
请问一下at the age of 与 by the age of 的区别.
还有最好给一下例句.
__the age of twenty,he had written two books.
答
at the age of 在某一岁数；在……岁时
by the age of 在某一岁数之前；到……岁时
Incredibly he shot a film at the age of 17.
不可置信的是他17岁就拍了部电影.
He must learn to be independent by the age of 18.
他18岁前必须学会独立.
你补充的问题答案用by