I think is very important for students to study by themselves in the school or at home.A.

问题补充：

I think is very important for students to study by themselves in the school or at home.

A. it B. this C. that

答案：

解析：考查代词it 做的是形式主语，真正的主语是后面的不定式。此题中I think后是一个宾语从句，it做主语，真正的主语为to study by themselves in the school or at home，句意：我认为对学生们来说在学校或在家里靠自己学习是非常重要的。故选A。