----Sixteen-year-olds should not be allowed to drive a car.--I agree. They are .A. too

问题补充：

----Sixteen-year-olds should not be allowed to drive a car.

----I agree. They are .

A. too serious

B. not serious enough

C. too calm

D. not enough serious

答案：

A. too serious

(答案→)B. not serious enough

C. too calm

D. not enough serious

解析：句意：16岁不应该允许开车。我同意，他们还不够认真。Enough足够，在修饰形容词时放在形容词后面，修饰名词时放在名词前面。再结合题意选B。