为使我国旅游饭店达到国际水平，1987年我国也相继成立（）。
A、星级饭店
B、饭店集团
C、现代化饭店
D、综合性饭店
参考答案：B
---______ the farmers discovered the entrance to the secret cave in the valley?
--- Totally by chance.
A．When was it that
B．How was it that
C．How it was that
D．When it was that
GPS全球定位系统使用（）颗卫星实现三维定位。
A.2
B.3
C.4
D.5
