完全双循环
自鸟类开始,心房与心室完全分隔,心脏分为左右心室和左右心房,在肺循环和体循环途径中动脉血和静脉血完全分开。提高了携带氧的能力
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
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