【题目】Some people get in touch with each other by mobile phones__________ others keep contact with each other by e-mail.
A. when B. before C. while D. since
在线课程【答案】C
【解析】考查连词：A. when当…时候B. before在…之前C. while当…时候，然而，虽然，D. since既然，句意：一些人通过手机彼此联系，然而一些人通过电子邮件联系。选C。