题目

What is the purpose of reading or studying? If you can't remember what you read or study, it will be a waste of time.   36    One useful aid that does help you remember what you study is to have a specific purpose or reason for reading. Why does a clerk in a store go away when your reply to her offer to help is, No, thank you, I'm just looking.? Both you and she know that if you aren't sure what you want, you are not likely to find it. But suppose you say instead, Yes, thank you. I want a pair of sun glasses. She says, Right this way, please.” It’s quite the same with your st一束光线自点P（1，1，1）发出，遇到平面xoy被反射，到达点Q（3，3，6）被吸收，那么光所走的路程是（ ）A．B．C．D．