from practice we can learn can't be learned from books
问题描述：
from practice we can learn can't be learned from books
from practice we can learn ____can't be learned from books
A who B that C which D what
last sunday i send him some flowers and cards as an e______of thanks .
能告诉为什么吗
答
d 理由 learn为及物动词,后面必须跟宾语
而此时后面应为宾语从句
从句中又缺少主语,所以用what
补充那个应该填上expression（表达）
上个星期天,我送给他一些花和卡片作为感谢的表达