Electronic devices such as iPods and headphones can do great harm to our hearing if improperly.
A. being used
B. used
C. to be used
D. having been used
网友回答
A. being used
(答案→)B. used
C. to be used
D. having been used
解析：句意：电子设备例如iPods和耳机，如果使用不当，能够对我们的听力造成极大的伤害。if后面的条件状语从句省略了they are ，根据句意用被动形式，故选B