下列运算正确的是[    ]

 A．a⁶a³=a¹⁸

B．（﹣a）⁶（﹣a）³=﹣a9

C．a⁶÷a³=a²

D．（﹣a）⁶（﹣a）³=a⁹

Patience is of great importance in our daily life. Once I waited a bus to come at a stop. 30 minutes past, but no bus came. Both upset and annoyed, I decided to walk on feet. But no sooner had I left when the bus arrived. I thought if I had waited for one more minute, I would have caught it. If I chose to take a next bus, I would have to wait for other 30 minutes. Only then do I realized my problem. Being impatient will possible waste all the effort that we have put it in. now whenever I am close to lose my patience, I’ll think of this experience.