The Internet is increasingly accessible at school and at home. _____many parents and teachers are sometimes not as prepared as we should be to warn children about Internet threats.

A．Actually

B．Generally

C．Surprisingly

D．Unfortunately

从所给的四个选项中，选择最合适的一个填入问号处，使之呈现一定的规律性（）

A．

B．

C．

D．