—How soon do you think the economy will recover?   —________?

A．What for

B．Who knows

C．Why not

D．How come

预购商品房预告登记后变更向一个以上房屋权利人颁发房屋权属证书时，每增加一本证书加收证书工本费（）元。

A.50

B.20

C.10

D.0