Children under fifteen are not permitted to see such kind of

Children under fifteen are not permitted to see such kind of movies 应该选什么?
Children under fifteen are not permitted to see such kind of movies _____ bad for their mental development.
A.that isx05x05x05B.that arex05x05C.as isx05x05x05x05D.as are
答案选的是B,我觉得应该是C,但不懂为什么.