填空，使用括号中的动词的正确肯定形式。
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The biology teacher (解释) a difficult concept.
Some students (记) notes during the lecture.
The headmaster (讲话) in the assembly hall.
A few classmates (准备) for the final exam.
The whole class (听) very carefully.
Two boys (争论) in the corridor.
The librarian (组织) the new books.
The football coach (展示) a new technique.
My best friend (写) an essay.
The university professors (评分) the papers.