Question

When you are planting trees, the trees ________ straight in the hole.

A．must put

B．must be put

C．are putting

D．is put

Answer 1

B

试题分析：句意为：植树的时候，树必须直立放到坑里。根据语境，句子的主语是“the trees”，是动作的承受者，应用被动语态。故选B。