21、（2018•荆门）---Your head teacher has set up a Wechat group．Could you tell____？
---It is more convenient to communicate with our parents．
A．when it was set up B．why did he set it up
C．what it is used for D．how did he set it up
21.C【解析】--你的班主任已经建立了一个微信群．你能告诉我它是用来做什么的吗？--它与我们的父母交流更方便了．根据Could you tell，可知本句考查了宾语从句的用法．在宾语从句中所使用的语序应该是陈述句语序，选项BD是疑问句语序，排除掉．再根据It is more convenient to communicate with our parents，和我们的父母联系起来更方便了，可知这里谈论的是它的用途，提问的话应该用what it is used for．故选C．