设函数$f\left(x\right)=\frac{a-2^x}{1+a·2^x}\left(a\in R\right)$是定义域上的奇函数，则a=____ ．

A: Hi, Peter. You look upset. What's wrong with you?

B: ____

A: For what?

B: My parents want me to go to music and art classes after school. ____ I like playing ball games very much. I want to be a famous football player.

A: You should tell them how you feel.

B: ____

A: What a pity! However, you shouldn't argue with them.

B: I had no other ideas. ____

A: ____ Maybe they will understand you.

B: I hope so. I'll have a try. Thank you.

A: You're welcome.

 在如图所示的电路中，闭合开关S，灯L不亮，电压表有示数。已知电路中各处均接触良好，除灯L和电阻R外，其余原件均完好。
(1)请写出发生上述现象的两个可能原因：____  或____  。
(2)为进一步确定原因，小华同学将一个电流表正确串联在该电路中，闭合开关S，观察电流表的示数情况。若电流表有示数，说明上述现象产生的原因是____ ；若电流表无示数，说明上述现象产生的原因是____ 。
(3)为进一步确定故障，小明同学将图14中的电压表并联在灯L两端，请判断他能否查找出电路的故障，并说明理由____ 。