题目内容：
根据下面内容，回答题：There are no inevitable outcomes of social class in child rearing. At the same time, there is no question that social class is important factor in how children are raised and the kind of adults that children become. Regarding social class, sociologists have found that parents socialize their children into the behaviors and norms of their work worlds. Members of the working class are closely super-vised and are expected to follow explicit rules at their jobs. If they do not follow the precise rules and do as they are told, they will not keep their jobs. Their experience., influences how they deal with their children. As a result, their concern is less with their children's motivations and more with their children's outward conformity. Thus they are more apt to use physical punishment in managing their children. On the other hand, middle-class parents, who are expected to take more initiative on the job, are more concerned that their children develop curiosity, self-expression, and self-control. They are also more likely to withdraw privileges or affection than to use physical punishment.
The word "explicit" means ___________. A．vague
B．difficult
C．confusing
D．clearly defined
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