题目

There is not enough oil in the world now. As time goes by, it becomes less and less, so what are we going to do when it runs out? Perhaps we will go back to using horses, carriages and bicycles. In the Second World War, some people didn’t use gas made from petroleum (石油) in their cars. They made gas from wood and plants instead. The car didn’t go fast, but they ran, so this was better than nothing. However, in the future, we can’t cut down all our trees to make gas; we need our trees for other things, too. Besides different types of gas, we can also use electricity to run ou下列说法正确的是（ ）A．一定温度下，同一物质的饱和溶液的质量数一定比其不饱和溶液的大B．碳酸钠的溶解度为40gC．固体物质溶解度随温度的升高而升高D．在一定温度下，搅拌可以改变硝酸钾的溶解度