单项选择题

A．75000
B．50000
C．25000
D．100000
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From his findings, Hay has established some flexible guidelines for parents of identical twins. One suggestion is for parents to ______ so that contact with other children will ______ accelerate language development.
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Twins, those who share the same placenta, are more likely to have social and learning problems, as well as ______.
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