题目

已知集合A＝B＝{0,1}，集合C＝{u|u＝xy，x∈A，y∈B}，则集合C的子集个数是                                                                                         ( ) A．4                               B．7 C．8                               D．16 It is usually warm in my hometown in March，but it_______ be rather cold sometimes． A．must        B．can        C．should        D．would