用于关闭早产儿动脉导管未闭的药物是（）。
A.地高辛
B.卡托普利
C.吲哚美辛
D.前列腺素
E.妥拉苏林
参考答案：C
The little boy ________ in the mud all the morning. No wonder he is dirty from head to foot.[ ]
A．has played
B．is playing
C．has been playing
D．was playing
启用STP的缺省情况下，拥有最小MAC地址的交换机将被选为根桥（therootbridge）
