题目

阅读下面短文，从每题所给的A、B、C、D四个选项中选出可以填入空白处的最佳选项。The morning was cool for a hike. I headed for the Appalachian Trail with my dog, Gracie. The first mile was1, just like climbing 50 steep flights of stairs. Then the road became2as it ran along a farmer's field. On the way down we passed a young couple out of3, who carried camping gear（装备）on their way up. I nodded, You only have about half a mile to go. A second later the woman4Hey, she said. Are you that guy?I5. What guy? I said. I had never been6, as a writer for a magazine某植物种群中，AA基因型个体占30%，aa基因型个体占20%，则： (1)该植物种群中A的基因频率是__________。 (2)若该种群中的植物自交一代，后代中AA、aa基因型个体分别占______、________，这时，A的基因频率是________。 (3)依据现代生物进化理论，这种植物在两年中是否发生了进化？______，原因是____________________________。 (4)现代生物进化理论认为，生物进化的基本单位是________，是否发生进化决定于__________。