Once an old man was walking in a street with his horse. It was raining hard. The old man was cold because he was walking in the rain. He wanted to stay in a restaurant.
   It was a quarter past three in the afternoon. The old man got to a small restaurant. A lot of people crowded in it. The old man couldn't come near the fireplace. He thought and thought.At last he said to the waiters, “ Take some fish to my horse.” The waiter and the other people were very surprised. The waitered said, “A horse doesn't eat fish.” The old man told the waiter, “ The horse is versatile. It can sing, dance and does all kinds of things. It can eat fish, too.” So the waiter took some fish to the horse.
   All the people in the restaurant rushed out to see the horse eat fish except（除了……之外） the old man. Now the old man sat beside the fire. After a while the waiter returned and said. “Your horse didn't eat any fish.” The old man said, “All right, take the fish back and put it on the table. I’ll eat it.”

①两灯泡并联；

②电流表测灯L₁的电流；

③闭合开关后，向A端移动滑动变阻器的滑片P，两灯均变暗．

下列各组词语中划线的字，读音全都正确的一组是（ ）

请写出A处主要反应的化学方程式____；C处观察到淡蓝色火焰，原因是____．