听力原文:W: I just found the most useful device at that new outdoor store, a water purifie
r.
M: A water purifier? You want to carry even more equipment with you on our hiking trips?
W: If it's lightweight and saves work, yes. And this one fits that description.
M: Really? I bet it takes up a lot of room.
W: Not at all. It's a straw. Much like the one you use to drink a soda or milkshake.
M: Really? That is small.
W: Ya. It's a plastic, and has a series of mineral and chemical filters that strain harmful microbes from water.
M: Yes. But how good a job can it do filtering the germs out of stagnant pond water or water from lake and streams?
W: It's fantastic. It makes the water entirely germ free.
M: But, what about salt or chemical pollutants that maybe in the water. Does it clean those out?
W: No, it doesn't remove salt and chemicals, but those are not really major concerns when we're out hiking and camping.
M: Mm. How long will a straw last?
W: For about 100 gallons, but don't worry about measuring that large amount of water. There is a built-in safety feature. The mineral and chemical filters become clogged long before the limit has reached and the straw stop drawing water.
M: 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.
Where will the special straw probably be most useful?
A.In restaurants.
B.On camping trips.
C.In science laboratories.
D.On car trips.