下列计算正确的是（　　）

A．（b²）³=b⁵

B．b²•b³=b⁶

C．b²+b³=2b⁵

D．b³+b³=2b³

_Could I go to the movie this Sunday, Dad?

_ Yes, you_____. But you ______ come back before nine.

A．should, can

B．must ,have to

C．can , have to

D．need, must