His supposition is good in theory _____ cannot be put into practice.

问题描述:

His supposition is good in theory _____ cannot be put into practice.
A.and
B.or
C.but
D.while

选C,
解析:根据意思,“他的猜想从理论上来说是很不错的,但是很难放到实践中去”故用but,不用别的.