I just don’t understand that leads to so many teenagers becoming addicted to playing compu

问题补充：

I just don’t understand that leads to so many teenagers becoming addicted to playing computer games.

A. why it does

B. what it does

C. what it is

D. why it is

答案：

A. why it does

B. what it does

(答案→)C. what it is

D. why it is

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