听力原文：M: I've just found the most useful device at that new outdoor store, a water puri

W: A water purifier. You want to carry even more equipment with you on our hiking trip？

M: If it's light weight and saves work, yes. And this one fits that description.

W: Really. I bet it takes up a lot of room.

M: Not at all. It's straw, much like the ones you use or drink a soda or milk shake.

W: Really, that is small.

M: Yea, it's plastic, and has a series of mineral and chemical filters that strain harmful germs from water.

W: Yes, but how good a job can it do filtering the germs out of motionless pond water, or water from lakes and streams.

M: It's fantastic. It makes the water entirely germ free.

W: But what about salt or chemical pollutants that might be in the water？ Does it clean those out？

M: No, it does not remove salt and chemicals, but those are really not major concerns when we are out hiking and camping.

W: Hmm, how long will a straw last？

M: For about one hundred gallons but don't worry about measuring that large amount of water. There is a built-in safety feature.

W: I think I'll get one for my camping trip this weekend, It'll sure be carrying a lot of water or having to boil it at the camp site.

(20)

A．In restaurant.

B．On car tripe.

C．In science laboratory.

D．On camping trips.