下表是不同时期府的南北地理分布情况统计表。出现表中变化的主要原因是（    ）

 从下面方框中选择适当的词填入短文中，使短文通顺正确（注意有些词要用适当的形式）。

    One day, Mr. White told the class to get ready for a hobby show. The students ____  the whole morning getting what they were going to show.
     All the students came back on time but Bob, the laziest ____ in his classmates' eyes. It seemed that it was very ____  for Bob to have a hobby. But to their surprise, Bob came back with many ____ stamps in his hand. Mr. White was very happy after watching them. However, Bob was going to ____ them back.
“Bob, you can't take them back until the others watch them this afternoon,” said Mr. White.
“But I am sorry they are my brother’'s,” he answered. “He doesn't want them to be out of our home for long. He's afraid that they will be ____  .”
“Bob, you should show some of your own ____  here, not someone else's. Mr. White became kind of angry.
But Bob's words made him even ____ . “Mr. White, it's true that I have a hobby. My hobby is watching my brother collecting stamps.”

某些化合物在形成时，不同元素的原子各自提供电子，形成共用电子对．在这种情况下，元素化合价的数值就是形成共用电子对的数目．在一个H₂S分子中，硫原子形成的共用电子对数目为（　　）

小猴有5个桃子，吃掉一个，列式为____。