The uniform makes us look like a bunch of clones, especially （） we are doing morning exercise in the playground. 

The uniform makes us look like a bunch of clones, especially （） we are doing morning exercise in the playground. 
A、since
B、which
C、as
D、when
正确答案：D
解析:词汇与结构部分\大学英语A\结构A\状语从句A