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【单选题】
Which of the following alternative explanations of the change in the cash value of children would most likely come from sociological economists?A.
Parents began to increase their emotional investment in the upbringing, of their children.
B.
Children's expected earnings over the course of a lifetime increased greatly.
C.
Compulsory education laws reduced the supply, and thus raised the costs, of available child labor.
D.
Changes in the law made available of indemnity for damages in accidental-death cases.
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【简答题】真核细胞染色质或染色体的主要化学成分有 和 。
【单选题】关于DNA和染色体的关系，不正确的是 [ ]
A.
DNA是染色体的主要化学成分
B.
染色体是DNA的主要载体
C.
一条染色单体含有一个双链DNA分子
D.
染色体和DNA都是遗传物质