When one makes new friends, don’t forget old ones.
A. to e up with
B. losing sight of
C. to keep track of
D. keeping in touch with
网友回答
A. to e up with
B. losing sight of
(答案→)C. to keep track of
D. keeping in touch with
解析：e up with意思是提出、 想出 lose sight of 看不见 keep track of 保持联系 keep in touch with保持联系。有了新朋友，别忘了老朋友。故选C。