（）体制即加密密钥公开，解密密钥不公开。
A.对称密码
B.秘密密码
C.传递密码
D.非对称密码
参考答案：D
Hurry up! The train_______. You know, it________at 8: 30 am.
A．leaves; leaves
B．is leaving; leaves
C．leaves; is leaving
D．is leaving; is leaving
