Trees---(plant)usually are planted in spring用括号内所给单词的适当形式填空

问题描述:

Trees---(plant)usually are planted in spring用括号内所给单词的适当形式填空

这句话有点奇怪吧?
不是已经填好了吗?
Trees are usually planted in spring.通常在春天种树.
usually应该放在be动词后,行为动词前.