题目内容：
根据下列材料，请回答题If someone is sleepwalkin9，they are walking around while they are asleep．Sleepwalking happens when a person is not fully asleep but not quite awake(清醒的)．Usually we move from our deepest levels(层面)of sleep to a lighter level and stay there．Sleepwalkers come right up to wake levels but do not fully awaken．It is at this time that they get up and walk．
The longer a person stays in deep sleep，the more time there is for the sleep to be broken That opens up the possibility(可能性)of being awakened(but not fully)and of sleepwalkin9．
Sleepwalking happens more often among young people than grown’ups because young people usually have more deep sleep．Up t07％of 5 to 12-year-olds sleepwalk，while only about 2％of grown．ups sleepwalk．We get less deep sleep as we are getting older and the possibility of sleep— walking is also reduced．
Sleepwalking may run in families,too．If one of your parents was a sleepwalker，you have about a 50％possibility of also being a sleepwalker·
The text is about． A．why sleepwalking happens
B．where sleepwalkers go
C．what sleepwalkers do
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