持续进行电解的条件是外加电压必须（）
A.大于分解电压
B.等于分解电压
C.小于分解电压
D.大于反电动势
参考答案：A
路堑开挖宜采用通道纵挖法的是（）。
A.长度较小的路堑
B.深度较浅的路堑
C.两端地面纵坡较小的路堑
D.不宜采用机械开挖的路堑
That's really typical（）John. He says he'll come but he never turns up.
A.for
B.of
C.to
D.with
