题目

A farmer once owned an old mule(骡子). One day, the mule fell into a nearby well, and it began to   21   and made a lot of loud noise. After carefully assessing the   22  , the farmer felt sorry for the mule, and   23   that neither the mule nor the well was worth the trouble of saving, then he called his   24  together and told them what had happened and   25   them to help shovel (铲) some dirt to bury the old mule in the   26   and put him out of his suffering.     Hearing many people coming to help, the old mule was   27 . But as the farmer and his n我国《婚姻法》规定禁止近亲结婚的理论依据是A．近亲婚配的家庭不稳定B．近亲婚配其后代必患遗传病C．近亲婚配后代患遗传病的机会增加D．遗传病都是隐性基因控制的