这个句子中系动词为什么变成be了

问题描述:

这个句子中系动词为什么变成be了
It is crucial that those new plants be environmentaly sound.
SORRY,全句是If we are ever going to protect the atmosphere,it is crucial that those new plants be environmentally sound.(在这里plants 不是植物,是工厂的意思)

在It is important/necessary/essential/crucial 等+that 结构中,that 从句里用(should)do .