Question

【题目】The bell rang _________ the teacher was explaining the experiment to the students.

A. until B. before C. while D. after

Answer 1

【答案】C

【解析】句意“老师正向学生们解释这个实验，下课铃声响了。”until直到；before在……之前；while表示当……时候，after在……之后。此处表示当老师正讲解实验时，铃声响了，故用连词while，故选C。