根据短文内容, 选择正确答案。

    Doing homework not only can help children master the knowledge they have learned, but also can train their abilities of finishing the work alone, planning the time and doing the duties. But some children don't like to complete the work. Why?

    Some children feel it is very difficult to do their homework, because they can't understand their teacher clearly, and cannot follow their teacher's teaching process (过程). Maybe there is something wrong with their intelligence.

    But some children's intelligence is normal. They are even cleverer, but they don't listen to the teacher carefully. It is hard for them to sit well and pay attention to anything.

    Some children love their teacher and then like the subject. Their interest depends on the teacher who teaches them. So every teacher should make children love you and the subject you teach. So they can do their homework happily.

扬声器是把　____ 　信号转换成　____ 　信号的一种装置，如图所示是扬声器构造示意图．当线圈中通过变化电流时，线圈受到　____ 　力作用，从而带动与线圈相连的纸盆　____ 　，于是扬声器就发出了声音．

1985年开始，我国把每年的____月____日定为教师节。

已知a＝ $\frac{1}{2016}\text{+}2015$ ，b= $\frac{1}{2016}\text{+}2016$ ，c= $\frac{1}{2016}\text{+}2017$ ，则代数式

2(a²＋b²＋c²－ab－bc－ac)的值是____．