满足条件{0，1}∪A={0，1}的所有集合A的个数是[ ]
A.1个
B.2个
C.3个
D.4个
答案：D
When he joined them in the work, he was disappointed at there _______ so little to do.
A．being
B．were
C．having
D．had
配送中心的作用有（）
A.存储功能
B.分拣功能
C.集散功能
D.衔接功能
E.流通加工功能
