下列各式计算正确的是[ ]

A．﹣3a+5b=2ab

B．5a+a=5a²

C．3a²b﹣6b²a=﹣3ab²

D．4a²b﹣3ba²=a²b

You should try to get a good night's sleep  ____ much work you have to do.      [ ]

A. however          

B. no matter      

C. although          

D. whatever