W: I just found the most useful device at that new outdoor store, a water purifier.
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
A. Factories
B. Inland seas
C. Mountain streams
D. Drug companies
Questions 1-10
All mammals feed their young. Beluga whale mothers, for example, nurse their calves for some twenty months, until they are about to give birth again and their young are able to find their own food. The behavior of feeding of the young is built into the reproductive system. It is a nonelective part of parental care and the defining feature of a mammal, the most important thing that mammals-- whether marsupials, platypuses, spiny anteaters, or placental mammals -- have in common.
But not all animal parents, even those that tend their offspring to the point of hatching or birth, feed their young. Most egg-guarding fish do not, for the simple reason that their young are so much smaller than the parents and eat food that is also much smaller than the food eaten by adults. In reptiles, the crocodile mother protects her young after they have hatched and takes them down to the water, where they will find food, but she does not actually feed
A. contrast the feeding habits of different types of mammals
B. describe the process by which mammals came to be defined
C. emphasize the point that every type of mammal feeds its own young
D. explain why a particular feature of mammals is nonelective
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