根据短文内容，从短文后的选项中选出能填入空白处的最佳选项，并在答题卡上将该项涂黑。每个选项限选一次。

When Andy came to school, he was surprised to find he was the first to arrive that day. “Where is Susie?” he thought. ____ She was the smartest student in the class and was always the earliest to class. Andy was always the second smartest and the second earliest.

In class, Andy learned that Susie went to visit her grandma in London and that she would not be back until Friday. ____  He was happy because he was the smartest kid and also the earliest to class for four days. He was sad because he could not see Susie, the girl he was secretly in love with.

Over the following days, Andy felt bad about being the smartest kid and the earliest to class. ____ .

____.  When Andy entered the classroom, he found Susie was already there. At that moment he decided one thing: Susie was the smartest girl in the class, and he was the smartest boy in the class. And that was enough.

计算：（6x²﹣xy）÷2x=____．

阅读下列材料：

材料一：“一九五三年将是我国进行大规模建设的第一年。”……“工业化——这是我国人民百年来梦寐以求的理想，这是我国人民不再受帝国主义欺负不再过穷困生活的基本保证，因此这是全国人民的最高利益。全国人民必须同心同德，为这个最高利益而积极奋斗。”

材料二：“用最高的速度来发展我国的社会生产力，实现国家的工业化和农业现代化，是总路线的基本精神……速度是总路线的灵魂。”

“人有多大胆，地有多大产”，“地的产是由人的胆决定的。”……社会主义建设虽然发生严重失误但仍然取得显著成就，涌现出大批先进人物。

请回答：

八达岭长城脚下，蜿蜒着一条铁路，它是中国人自行设计和施工的第一条铁路干线，这条铁路是（    ）