围堰的分类中,下列属于按其使用材料分类的是( )。
A.土石围堰
B.混凝土围堰
C.过水围堰
D.草木围堰
E.横向围堰
参考答案:A,B,E
小红在研究串联电路电流的特点时,共做了三次实验,(如图所示)记录数据如下表:
(1)小红在测量过程中,有一次是错误的,错误的一次是:_____.
(2)这次错误的原因可能是_____.
Athens _____ the birthplace of western civilization.[ ]
A. are known as
B. is known as
C. are known for
D. is known for