不同物种之间存在着地理隔离,同一物种的种群之间存在着生殖隔离。
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The girl is arguing with her boyfriend ________ how to spend the money.
The screen standing _______ the couple is that they are from different countires.
People close their windows at night in an attempt to shut _________ the sound of gunfire.
My teacher always gives me some advice ________ my study.