Last year I caught the baby cuckoo and put 56. ______
it in a cage outside. Later its mother flew from the cage 57. ______
with food in her mouth. I was happy to see this, because of 58. ______
the mother bird knew much better than I did to feed her 59. ______
baby. But the following morning I found the baby bird60. ______
died. I told the story of my bird to my biology teacher 61. ______
and he explained that what had happened. A mother 62. ______
cuckoo, finds her baby in a cage, will bring it poison63. ______
food. She believes it is good for her baby to die than to 64. ______
live in a cage. I still feel sorry for what I do to the bird.65. ______

重复的产生机制及遗传学效应。