问题补充：
Cell phones by more and more teens and many new functions to them nowadays.
A. are using, have added
B. is used, are adding
C. are being used, have been added
D. being used, were added
答案：
A. are using, have added
B. is used, are adding
(答案→)C. are being used, have been added
D. being used, were added
解析：可联系答.案.网客服索取。
