We must known to all that smoking is harmful to heart.A. thisB. thatC. itD. the matter

问题补充：

We must known to all that smoking is harmful to heart.

A. this

B. that

C. it

D. the matter

答案：

A. this

B. that

(答案→)C. it

D. the matter

解析：句意：我们必须要让所有人知道吸烟已对心脏有害。it做形式宾语代替后面that引导的宾语从句。故选C。

考点: 考查代词的用法。