单项选择题
A．has come into being B．had come into being C．came into being D．comes into being
50（）A．butB．whileC．andD．however
单项选择题50（）
A．but B．while C．and D．however
51（）A．park lotB．park lotingC．parking lotsD．park lots
单项选择题51（）
A．park lot B．park loting C．parking lots D．park lots
49（）A．helpingB．to helpC．helping toD．to help to
单项选择题49（）
A．helping B．to help C．helping to D．to help to
