二月初以来，我国各地旱区认真落实国务院抗旱工作会议精神，采取一切更加有效的措施，全面掀起抗旱保苗促春管热潮，为夺取今年夏粮丰收奠定了基础，实施人工增雨是缓解旱情有效手段，在空中喷洒干冰是人工增雨的一种方法．干冰使空气中的水蒸气变成小冰粒，这是因为水蒸气发生了（　）​

    Bill is an English boy. He is twelve. He lives in China with his family. There are four people in his family. They are his father Jack Cliton, his mother Catherine and his little sister Abby. He has a yellow dog. Its name is Barbi. His father is mending his bike. What is Bill doing? Ah, he is doing Chinese homework. He can't speak Chinese very well. But he loves Chinese very much. Bill's father works in middle school. He is an English teacher. His mother is in a TV factory. Bill and his sister go to the same school.

有下列四个命题：

①三个点可以确定一个平面；

②圆锥的侧面展开图可以是一个圆面；

③底面是等边三角形，三个侧面都是等腰三角形的三棱锥是正三棱锥；

④过球面上任意两不同点的大圆有且只有一个．

其中正确命题的个数是（  ）

阅读下列材料，回答下列问题：

材料一：科学家将一种矮秆（抗倒伏）但不抗锈病的小麦与另一种高秆（不抗倒伏）但抗锈病的小麦做亲本进行杂交．后代中出现了矮秆抗锈病、矮秆不抗锈病、高秆抗锈病、高秆不抗锈病四种类型，选矮秆抗锈病类型繁殖培育，若干代后，获得了矮秆抗锈病小麦新品种．

材料二：科学家利用航天技术搭载普通椒的种子，返回地面后再进行选育，培育出果实大、口感好、产量高的太空椒．

材料三：新疆的哈密瓜甜度大，有人将其引进到山东来种植，其甜度大大降低．

成都某公司的小夏急着去北京签定一份合同，第二天早上必须赶到。他应该选择的交通运输方式是（  ）