the prices of water have_______for years .

问题描述:

the prices of water have_______for years .
A.remained unchanged B.kept unchanged
C.stayed unchanging D.remained unchanging
答案我知道,只是想知道为什么不能用kept unchanged表保持不变的状态.把unchanged当成形容词的话不行吗?有keep+adj.
我觉得B也对

remain unchanged可以表示自然呈现的状态,keepunchanged 表示机构或人员在有意努力保持的状态,如果用keep,应当用被动语态