世界上面积最大的淡水湖是( )
A.贝加尔湖
B.里海
C.密歇根湖
D.苏必利尔湖
答案:D
Usually, Betty _______ in colourful T-shirts in summer. [ ]
A. wears
B. is dressed
C. is wearing
D. dresses
键码的定义:在实体集的范围内唯一标识______。