A、In restaurant. B、On car tripe. C、In science laboratory. D、On camping trips. D

M: I’ve just found the most useful device at that new outdoor store, a water purifier.
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.