Parents should stop blaming themselves because there’s not a lot they can do about it. I mean the teenager problem. Whatever you do or however you choose to deal with it, at certain times a wonderful, reasonable and helpful child will turn into a terrible animal.
B．a headmaster of a middle school
C．a parent with teenage children
D．Parents are at fault for the change in their children.
在边长为1的等边三角形ABC中，设
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的值为
