Before signing up for next year's courses,《the students' schedules must be approved by their advisers.》
Before signing up for next year's courses,《the students must have their schedule approved by their advisers.》
正确答案是第2句,请问为什么。
我觉得第1句,我的理由是被证实,所以must be approved ,是被动句子,但为什么错呢。
麻烦讲解下。