it is extremely urgent that they ___ from the mountain before dark

Question

A shall be rescued Bwill be rescuedC berescued D must rescue 麻烦讲清楚点！

Answer 1

只能选C
这是一种省略了should 的虚拟语气。
句型是：it is +adj+that sb (should) do sth....
常见的形容词有 necessary 、imperative 、urgent 等
翻译：他们急需在天黑之前被从山上救下来。