(2013·贵州模拟)Tom, clean up the broken glasssomeone walks on it.A. sinceB. whenC. beforeD. as

(2013·贵州模拟)Tom, clean up the broken glass someone walks on it.
A. since
B. when
C. before
D. as

A. sinceB. whenC. beforeD. as解析：选C。考查状语从句。句意: 汤姆, 把碎玻璃收拾干净, 以防有人踩上。此处before意为“以防; 免得”, 引导时间状语从句。【变式训练】①(2013·重庆模拟)—Hello, can I speak to Mr. Smith?—I’m sorry, but it is 3 weeks he worked here.A. before B. since C. after D. while选B。考查状语从句。句意: ——喂, 我可以跟史密斯先生通电话吗? ——很抱歉, 他不在这里工作已经有三周了。此处考查句型: It is +一段时间+since从句(使用一般过去时)。此处since从句使用的是延续性动词, 表示该动作停止到现在多久了。②It was nearly an hour the sleeping pill effect.A. when; took B. before; tookC. since; takes D. before; would take选B。考查状语从句和时态。句意: 过了几乎一小时那片安眠药才起作用。此处before引导一个时间状语从句, 句型为: It was some time before. . . did. . . 表示“过了多久才……”。

这个答案应该是对的