In the past few years, a great many teachers have found very important to teach their stud

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A. this
B. that
C. one
(答案→)D. it
解析：考查形式宾语。在英语中只有it可以作为形式主语，形式宾语。在本句中It作为形式宾语，代替真正的宾语to teach their students how to learn.句意：在过去的几年里，很多老师都发现教会学生如果学习很重要。故D正确。