The rich often ______ the poor in our village.

In 1638, John Harvard donated some money and about four hundred books to a new university. This was the beginning of the library at Harvard University. The gift was so important that the university was named for John Harvard.
Thomas Bray began the first free lending library in the late 1600s. He set up more than 30 or these libraries in the American colonies. However, the idea for this kind of free library ended when Bray died in 1730. In 1731, Benjamin Franklin and some friends started the first subscription（订阅费） library in the United States. In a subscription library people pay money to become members, but they may borrow the books without paying again.
In the United States, every child had a free education. This idea soon led to free libraries. One of the first libraries that used tax money to buy books was a library in Peterborough, New Hampshire. This library was set up in 1833.

科技小组的同学们没计了如图甲所示的恒温箱温控电路（用于获得高于室温，控制在一定范围内的“恒温”），包括工作电路和控制电路两部分。其中，R′为阻值可以调节的可变电阻。R 为热敏电阻（置于恒温箱内），其阻值随温度变化的关系如图乙所示，继电器线圈电阻50欧姆。

材料一：

材料二：

有四位同学对某化学式的描述是：甲表示一种物质；乙表示一个分子；丙表示该物质由不同种元素组成；丁表示一个分子由二个原子构成。他们描述的化学式是（ ）