Any habit slows down your silent reading to the speed at which you speak or read aloud

问题补充：

Any habit slows down your silent reading to the speed at which you speak, or read aloud, is inefficient.

A. which

B. /

C. that

D. who

答案：

A. which

B. /

(答案→)C. that

D. who

解析：句意:任何一个习惯它可以减慢你的默读的速度达到说话或者大声读的速度，那么这个习惯就是效率低的。这里是定语从句，先行词是habit，关系词在定语从句中作主语，不能省略，因为先行词有any修饰，故用that，故选C。