1 . _________ (专心于) on my homework, I didn’t notice they had sat down behind me. (根据汉语提示单词拼写)
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2 . I was ____________(集中注意) on writing a letter when the telephone rang.
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3 . Only if you __________(集中) on your study can you get good grades.
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4 . You should c_____________ on your work when you study. (根据首字母填空)
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