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

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：本题的主语是动词短语在河里游泳，在英语中可用形式主语it来表示，真正的主语写在后用动词不定式，故选C。