The water purification method ？ -remove all subtances
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-only removes suspended impurities
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-use heat
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-add chlorine water
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Which cause-and-effect relationship in “broken chain” relates to the theme "by others, we ourselves"?

Read the excerpt from "mending wall." we keep the wall between us as we go. to each the boulders that have fallen to each. and some are loaves and some so nearly balls we have to use a spell to make them balance: "stay where you are until our backs are turned! " we wear our fingers rough with handling them. oh, just another kind of out-door game, one on a side. it comes to little more: there where it is we do not need the wall: he is all pine and i am apple orchard. what does the line “and some are loaves and some so nearly balls” refer to?

Some organisms have a large geographic range. for example, the norway rat lives on every continent except antarctica. a population of norway rats is the number of rats in one particular area. do you think it’s scientifically possible for a population of norway rats in north america to carry different genetic mutations than a population of norway rats in africa? do you think it’s possible that they carry some of the same mutations? what types of information can scientists learn by studying the genomes of these two populations of rats?