下列关于黄土高原的地表特征，描述正确的是[ ]
A．起伏和缓、开阔坦荡
B．山水环绕、沃野千里
C．沟壑纵横、地面破碎
D．雪山连绵、冰川广布
答案：C
——Why are the housing prices in big cities going up all the time?
————One reason is that people are__________ into overcrowded cities in great numbers.
A．breaking
B．filling
C．pouring
D．hurrying
百日咳病人进行隔离，至痉挛性咳嗽出现后隔离（）天。
A、10
B、20
C、30
D、40
