被动语态的选择题

被动语态的选择题
It is said that it is no use growing this species of plants in this area,which will be rather difficult—
为什么添 to care for, 不应该是被动用to be cared for?表示被照顾?
which 后面的be 应该是which 的谓语吧，不定式的被动怎么体现呢？