题目

下列属于先天性行为的是(     )       A．家中饲养的小猫到固定的地方大小便       B．青蛙捕食害虫       C．蚯蚓走迷宫       D．兀鹫会用石块将鸵鸟蛋砸碎来享受美味 答案：B．In the past, the workers _____ do a lot of hard work.                  A. forced                          B. forced to                C. were forced to