Long bus rides are like television shows .They have a beginning ,a Middle and an end –with commercials thrown in every three or four minutes .The commercials are unavoidable .They happen whether you want them or not .Every couple of minutes a billboard glides by outside the bus window . “buy super clean toothpaste”. “Drink Good’n Wet Root Beer .””Fill up with Pacific Gas .”Only if you sleep ,which site equal to turning the television set off ,are you spared the unending cry of “You Need It ! Buy It Now !” The beginning of the ride is comfortable and somewhat exciting ,Even if you’ve traveled that way before .usually some things have changed-new houses ,new buildings ,sometimes even a new road .The bus driver has a style of driving and it’s fun to try to figure it out the first hour or so . If the driver is particularly reckless or daring ,the ride can be an thrilling as a suspense story .Will the driver pass the truck in time Will the driver move into the right or the left –hand lane After a while,of course,the excitement dies down .sleeping for a while helps pass the middle hours of the ride .Food always makes bus rides more interesting .But you’ve got to be careful of what kind of foodyou eat .Too much salty food can make you very thirsty between stops. The end of the ride is somewhat like the beginning .You know it will soon be over and there’s a kind of expectation and excitement in that .The seat ,of course ,has become harder as the hours have passed.By now you’ve sat with you legs crossed ,with your hands crossed behind your head .the end comes just at the right time . There are just no more ways to sit.

What is the purpose of this passage ()

A．To give the write’s opinion about long bus trips

B．To persuade you to take a long bus trip

C．To explain how bus trips and television shows differ

D．To describe the billboards along the road

在开启和关闭时省力，水阻较小，阀体比较短，完全开启时，其阀板不受流动介质的冲刷磨损的阀门是（）。

A．止回阀

B．截止阀

C．闸阀

D．球阀