单选题 The females in the rat population were ______ by the high population density.
【正确答案】 B
【答案解析】考查动词修饰的方法。此句意为“在老鼠的种群之中，雌性受高种群密度的影响最大”。be affected by意为“受……的影响”；副词seriously修饰动词affected；the most修饰seriously，表示严重的程度。