问题补充：
My sister text messages to me on the mobile phone,but now she e-mails on QQ.
A. is used to send ; used to send
B. is used to sending ; used to send
C. used to send ; is used to sending
D. used to send ; used to send
答案：
A. is used to send ; used to send
B. is used to sending ; used to send
(答案→)C. used to send ; is used to sending
D. used to send ; used to send
解析：句意：我的妹妹过去常常用手机给我发短信，但现在她习惯了发QQ邮件。Used to do sth过去常常做某事；be used to doing sth习惯于做某事，所以选C。
