It is difficult for parents of nearly every family to teach their children to be responsible for housework,    11   with one of the following suggestions, you really can get your children to help at home.

If you give your children the    12    (impress) that they can never do anything quite right, then they will consider    13    to be unfit or unable persons.  14  children believe they can succeed, they will never become totally independent.

My daughter Carla’s fifth grade teacher made every child in her class feel special. When students received ___15_( little) than a perfect test score, she would point __16___ what they had mastered and declared firmly they could learn what they had missed.

You can see the same technique when you evaluate your child’s  work at home. Don’t always scold and give lots of praise    17   . Talk about what he has done right, not about what he hasn’t done. If your child completes __18___ difficult task, reward him    19    a Sunday trip or a ball game with Dad. Learning is a process of trying and failing and trying and 20   (success)in the end. If you teach your children not to fear a mistake of failure, they will learn faster and achieve success at last.

已知单头圆柱蜗杆传动的蜗轮齿数为80，则其传动比为（）

A.1/80

B.1/40

C.40

D.80