问题补充：
---Sixteen-year-olds can drive their cars to school?
---No. They shouldn’t to drive their cars to school because are not serious enough.
A. allow
B. allowed
C. Be allowed
D. Have allowed
答案：
A. allow
B. allowed
(答案→)C. Be allowed
D. Have allowed
解析：考察被动语态,这句话总他们是被允许的对象,故用被动语态,选C.
