C

    Everyone has worries. How do you deal with your worries? There is always something you can do to help yourself feel less worried. Sitting there worrying is no fun and it won't solve your problems.

    Grades at school are often a top worry for children. If you worry most about grades, ask yourself these questions:

    ● Why are grades important? What do grades mean to me?

    ● How do I get ready for class? Do I go over my notes even when there isn't a test?

    ● Do I have a good place to do my homework?

    ● Have I tried different ways of studying?

    If your worry is about a fight you had with your friend, you might write down all the things you could do ---- write a note to him or her, invite him or her to watch a basketball game, say sorry to him or her and so on. Once you have a list of things you could do, you can choose one thing that could get your friend back.

    You can ask for help when you're worried. You can find someone to talk to, such as your parents, friends, and teachers.

已知 $\frac{x}{x^2+1}$ = $\frac{1}{2}$ ，求 $\frac{x^2}{x^4+1}$ 的值．

解：由 $\frac{x}{x^2+1}$ = $\frac{1}{2}$ 知x≠0，所以 $\frac{x^2+1}{x}$ =2，即x+ $\frac{1}{x}$ =2．

∴ $\frac{x^4+1}{x^2}$ =x²+ $\frac{1}{x^2}$ =（x+ $\frac{1}{x}$ ）²﹣2=2²﹣2=2，故 $\frac{x^2}{x^4+1}$ 的值为 $\frac{1}{2}$

评注：该题的解法叫做“倒数法”，请你利用“倒数法”解下面的题目：

已知 $\frac{x}{x^2-x+1}$ = $\frac{1}{7}$ ，求 $\frac{x^2}{x^4+x^2+1}$ 的值．

下列可作为二氧化硫检测植物的是（）

如图是人类某一家族甲种遗传病和乙种遗传病的遗传系谱图（设甲遗传病与A和a这一对等位基因有关，乙遗传病与另一对等位基因B和b有关，且甲乙两种遗传病至少有一种是伴性遗传病）．请回答有关问题：

（1）甲病的遗传方式是____ ，个体5基因型是____ ．

（2）个体8的乙种遗传病致病基因最初来源于图中的____ ．

（3）若个体3和个体4再生一个女孩，则该女孩表现正常的概率为____ ．

（4）若个体8和个体9结婚，则生下一个患甲病小孩的概率是____ ．