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31. An water, even rain water, contains dissolved chemicals those scientists call “salts”.
trước water hok có mạo từ\Rightarrow bỏ an
32. Sea water, in contrast to the water we use daily, contains unacceptable amounts of dissoloved chemicals, which makes it is too salty for human consumption.\Rightarrow bỏ the

33. Scientists seek the answers about the mysteries of undersea world with full awareness that little about the oceans has understood.\Rightarrowhave

34. What arouses the scientists’ curiosity is not so many why the ocean is salty, but why it is not fresh like the rives and stream that pour into it.\Rightarrowmuch

35. If the salt in the sea could be removed and spread evenly over the Earth’s land surface, it will form a layer more than 500 feet thick, about the height of a 40 – storey office building.\Rightarrow is