It may be necessary to stop（）(每隔一定时间) in the learning process and go back to the difficult points in the lessons.
正确答案:at intervals
答案解析:有
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中学特岗教师招聘
中学特岗教师招聘
It may be necessary to stop（）(每隔一定时间) in the learning process and go back to the difficult points in the lessons.
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