介词填空：( )his letter I konw he is studying English in the English corner

from
固定词组
know....something...from...something
从。。。之中得知某事
中英文词组互译字典

By

know by
通过＊＊＊认识

From

from是绝对没问题的，可能还有其他答案。

from

from