化简 $\frac{2x+2y}{5a^{2}b}\cdot \frac{10a{b}^2}{x^2-y^2}$ 的结果为____。

    It's very important that we all recycle. In nature, everything can be1again. For example, when an animal dies, it becomes 2animal's food. Nothing is wasted. But humans have created things like plastic bags 3can't be broken down by nature. Our rubbish kills animals and 4water and soil. 5we continue making too much rubbish, the problem will only get worse. If nature can't reuse the rubbish, we must recycle6.

    We should clean up the rubbish we've made because nature can't.

    Recycling is also the right thing to do for another reason. The earth is rich in natural materials like water and trees,7these materials are not endless. We use up our natural materials much8than the earth is able to reproduce them. For example, each year we cut9more that 6,000 square miles of forest. But it takes about 25 years 10a new tree to grow.

    Recycling can help us save the earth, so let's take action right now.

It was difficult __________ something because it was dark.