Question

【题目】Don't touch the instruments in the laboratory ________ the teacher allows you to do that.

A．unless B．when C．though D．because

Answer 1

【答案】A

【解析】

试题分析：句意：在实验室不要碰仪器, 除非老师允许你这样做。unless连词，除非，引导条件状语从句。所以选A。