新生儿应接种
A．麻疹疫苗B．乙型脑炎疫苗C．脊髓灰质炎疫苗D．百、白、破混合制剂E．乙肝疫苗
参考答案：E
They became friends again that day. Until then, they _____ to each other for nearly two years. [ ]
A. didn't speak
B. hadn't spoken
C. haven' t spoken
D. haven' t been speaking
DDN各节点间数字信道的建立要考虑其网络拓扑，网络中各节点间的数据业务量的流量、流向以及网络的安全。（）
