若 $a<b$ ，则下列各式一定成立的是（      ）

阅读短文，下列问题

      A boy goes to the cinema. He buys a ticket and goes in. But after two or three minutes he comes out. He buys a second ticket and goes in again. After a few minutes he comes out again and buys a third ticket. Two or three minutes after that he comes out the fourth time and asks for another ticket. The girl says to him, “Why are you buying all these? Are you meeting friends in the cinema all the time?”

     “No, I'm not doing that,” the boy says. “But a big woman always stops me at the door and tears(撕掉) my tickets.”

选择正确的解释。

白：A.雪或乳汁那样的颜色；

B.清楚；

C.亮；

D.没有价值；没有效果和意义

E.陈述，说明；

F.指字形或字音有错。