A：四羊方尊
B：司母戊鼎
C：青铜立人像
D：毛公鼎
为安全起见，妈妈为小明买了一块浮板辅助练习游泳．妈妈认为浮板能漂在水面上是因为它轻，小明认为妈妈的说法不对，科学的说法是因为浮板的密度比水的密度小．为验证自己的说法，小明设计了如下实验：
You'd better ask a ______, such as your aunt or sister, to look after your children while you are away.
