按人们外出旅游的目的归属，可将旅游者划分为三种基本类型，即消遗型、差旅型和（）
参考答案：家庭及个人事务型旅游者
It is so difficult a question _____ none of the kids could work it out. [ ]
A. as
B. that
C. which
D. ×
社会保险
