小阳同学在厨房里，发现3包用相同塑料袋装着的白色粉末，询问后得知是淀粉、苏打（碳酸钠、Na₂CO₃）和小苏打（碳酸氢钠、NaHCO₃）。为了区分它们，把3种白色粉末分别标号为A、B、C后，设计了如下探究过程：

查询资料：碳酸氢钠在加热时能分解成碳酸钠、二氧化碳和水，而碳酸钠不会分解。

    In the United States, children start school when they are five years old. In some states they must stay in school1they are sixteen. Most students are seventeen or eighteen years old when they2secondary(中等的)schools. There are two kinds of schools in the United States: public(公立的)schools and private(私立的)schools.3children go to public schools. Their parents do not have to4their education because the schools5money from the government(政府).If a child goes to a private school, his parents have to get enough money for his schooling. Some parents still6private schools, though they are much more expensive.

    Today about half of the high school students7universities(大学)after they finish the secondary school. A student at a state university does not have to pay very much if his parents8in that state.

    But many students9while they are studying at universities. In this way they10good working habits(习惯)and live by their own hands.

“我国第一个五年计划取得了重大成就。”下列史实中可以证明这一结论的是(      )
①武汉长江大桥建成　②开展了大炼钢铁的群众运动　③长春汽车制造厂、鞍山钢铁公司等重工业企业投产④新藏、青藏、川藏公路及宝成铁路修通