完形填空，先通读下面的短文，掌握其大意，然后在每小题所给的四个选项中，选出可以填入空白处的最佳选项，并在答题卡上将该项涂黑。

    I sat with my friend in a well-known coffee shop. As we enjoyed our coffee, a man entered and sat down beside us. He called the waiter and ordered, "Two cups of coffee, 1of them there on the wall." We heard this with great 2 and saw that he was served with one cup of coffee but he paid for two. As soon as he left, the waiter3 put a piece of paper on the wall saying "A Cup of Coffee". While we were still there, two other men had two cups of coffee but paid for three. 4 the waiter did the same thing. It seemed that this was usual at this place. However, it was something strange for us. Since we had nothing to do with the5, we finished our coffee, paid and left.

    After a few days, we again had a 6to go to this coffee shop. While we were enjoying our coffee, a man entered. The way this man was dressed did not match the 7 of this coffee shop. As he seated himself, he looked at the wall and said, "One cup of coffee from the wall." The waiter served coffee to this man with the same8. The man had his coffee and left without paying. The waiter took off a piece of paper from the 9 and threw it in the dust bin. Now there was no 10 for us. The great kindness for the people in need shown by the people of this town filled up our eyes with tears.

①A所表示的元素位于元素周期表的第____周期，C是氯元素对应的粒子，其符号是____.

②A、B、C中属于同种元素的粒子是____;A和B两种粒子的____;相同，所以它们具有相似的化学性质。