阅读下面材料

【材料一】按一定顺序排列的一列数称为数列，记作：{a_n}（n属于正整数）．数列中的每一个数都叫做这个数列的项，排在第一位的数称为这个数列的第1项

（通常也叫做首项），记作：a₁；排在第二位的数称为这个数列的第2项，记作：a₂；…；排在第打位的数称为这个数列的第n项，记作：a_n．

【材料二】如果一个数列从第二项起，每一项与它的前一项的差等于同一个常数，这个数列就叫做等差数列．这个常数叫做等差数列的公差，公差常用字母d表示．

例如：数列10，15，20，25是等差数列．

如果数列a₁，a₂，a₃，…，a_n，…是等差数列，那么a₂﹣a₁=d，a₃﹣a₂=d，…，

a_n﹣a_n﹣1=d．即：a₂=a₁+d，a₃=a₂+d=a_l+d+d=a₁+2d，a₄=a₃+d=a₁+3d，…．

根据上述材料，解答问题

三角形的三个外角之比为2：3：4，则与之相应的三个内角之比为（　　）

 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.”