题目

Friendship is one of the most important     61      (thing) in everyone's life.   62   is very difficult to find a better definition(定义) of friendship. A true friend is the person 63       can share all our sadness and double all our happiness. In time of trial(艰苦) , he or she is always at our side to give us his or her help and comfort. Knowing how    64 (value) friendship is, we should be very careful with our choice of a friend. We should choose those people with a good character 65   our friends, but we must try to avoid 66   (make) friends with a 可遗传的变异是由什么引起的（ ）A. 个体生长很快 B. 个体发育很好C. 遗传物质发生了变化 D. 生存环境发生了变化