As a rule，domestic servants doing odd jobs are paid _________.
A.by the hourB.by hourC.by an hourD.by hours在线课程A
by表示计量单位, 意为“以……计”.若后接单数可数名词，其前要用定冠词；若后接复数名词或抽象名词，通常用不定冠词.hour为单数可数名词，表示计量其前要用定冠词，故答案为A.例如：They are paid by the hour／the month．
他们所得报酬按小时(月)计算.
Are bananas sold by weight or at how much a piece?香蕉是按重量出售，还是按多少钱一根出售?