—is very interesting to swim in the river in summer but it’s dangerous.A. ThisB. ThatC. It

问题补充：

—is very interesting to swim in the river in summer,but it’s dangerous.

A. This

B. That

C. It

D. He

答案：

A. This

B. That

(答案→)C. It

D. He

解析：句式：It is adj to do sth做某事怎么样。本结构中it做形式主语，指代下文不定式内容，其它选项无此用法。故选C。