They make up about 45% to 50% of the volume of blood is red cells.

红细胞占血液体积的,45%到50%

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As it does that it changes the volume of the heart and gives the - creates the pressure that moves blood around your body, so it has that muscular system.

这使心脏的体积发生变化,产生了足以使血液流遍全身的压力,这就是心脏中有肌肉系统的原因

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