2014高考英语查缺补漏集中营： 阅读理解
——决定成败
科普常识类
below is a selection from a popular science book.
if blood is red，why are veins(静脉) blue?
actually，veins are not blue at all.they are more of a clear，yellowish colour.although blood looks red when it's outside the body，when it's sitting in a vein near the surface of the skin，it's more of a dark reddish purple colour.at the right depth，these bloodfilled veins reflect less red light than the surrounding skin，making them look blue by comparison.
which works harder，your heart or your brain?
that kind of depends on whether you're busy thinking or busy exercising.your heart works up to three times harder during exercise，and shifts enough blood over a lifetime to fill a supertanker.but，in the long run，your brain probably tips资源难易程度:★★★★★★★★★★★★★★★
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