The Alpine snowdrop, a flower native to high-altitude mountain ranges, relies heavily on the hummingbird species Trochilus montanus for pollination. In the late 1800s, several of these flowers were relocated to a valley region devoid of T. montanus. Yet, driven by evolutionary forces, nature's intricate relationships have a propensity to reestablish themselves. By the mid-1900s, researchers noticed not only the appearance of T. montanus in the valley but also that the Alpine snowdrop was predominantly pollinated by them.
Which choice best describes the function of the third sentence in the overall structure of the text?
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