电池串联后的内阻等于每个电池内阻的（）
A、和
B、差
C、倒数和
参考答案：A
You must ____________ a good mountain bike.[ ]
A. had
B. have
C. has
D. having
计价规范P171的阀门、水表与给排水册的清单项目有重复，如何理解？
