题目内容：
Which of the following is derivable from Bowlby' s work?
A．Mothers should not send their children to day care centers until they are three years or olde B．Day care nurseries have positive effects on a child's developmen
C．A child sent to a day care center before the age of three may have emotional prob-lems in later lif
D．Day care would not be so popular if it has noticeable effects on a child's personalit
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