漏洞进水口附近的水流易形成()。
A.旋涡
B.静水
C.主流
D.横向环流
参考答案:A
Four-fifths of the crop _____.[ ]
a. are ruined
b. was ruined
c. were ruined
d. have been ruined
由初步E-R图构成基本E-R图,其主要任务是()。
A.消除不必要冗余
B.消除属性冲突
C.消除结构冲突和命名冲突
D.B)和C)