Sheridan is a town in Indiana, USA. There are lots of trees near the public schools in the town. Their leaves turn sunlight into energy (能量).

In Sheridan, the sun not just provides energy for plants. It keeps schools running, too. The schools use solar panels (太阳能电池板) to turn sunlight into energy.

The science behind solar energy is not new. But Sheridan Community Schools is the first school district (学区) in Indiana to be completely solar-powered. The district finished putting in solar panels for all three of its schools in 2016. Some of the panels can turn to follow the sun across the sky.

In 2008, fewer than 1,000 schools used solar power. By 2014, there were 3,727 schools with solar panels in the USA. These numbers come from a report by the Solar Foundation. Roxie Brown, a program director there, said that the number of schools with solar panels has continued to go up since 2014.

Solar energy has some advantages over other energy sources (来源). Sunlight is a renewable source, which means it won't run out. Solar panels don't harm the environment. Also, sunlight is free. So by using solar power, schools can save money on energy costs.

Brown thinks more schools should run on solar energy.“The sun is Earth's energy source,” she says. “We’re trying to make it the energy source for our houses, cars and schools, too.”

But using solar energy isn't always easy. Solar panels can be expensive to put in. The panels also take up space. But for many schools, going solar is worth it.

①Have you ever paid for educational podcasts（播客）or live videos? Ask some people and most of them will say yes. “Pay-for-knowledge” has been a fashionable thing these years. Everything you think of can be found online, skills of talking, designing, computer programming and so on.

②Why is “Pay-for-knowledge” industry developing so rapidly? First, its development is based on the Internet. With a fast network and a smart phone, anyone who has passed the identity（身份）check can be an online teacher, and anyone with an online account（账户）can buy “Pay-for-knowledge” products that he or she wants at a good price. Second, people are afraid to miss any information. They hope for more useful information which is usually at the hands of experts. Moreover, the need to learn new skills in today’s job market also pushes people to learn on such educational podcasts.

③The industry of “Pay-for-knowledge” has proved to be a great way of making money. It promises possibilities of turning information into money. It is good for the development of our country and it can help sellers make lots of money. Besides, buyers can enjoy self-growth from it. What’s more, this is a reflection（反映）of people’s respect for knowledge and talents.

④However, “Pay-for-knowledge” also causes a few problems. For one thing, the market is full of eye-catching words such as “How to be a good CEO?” which sound like if you pay for it, you are sure to succeed. For another, a large number of customers buy them just for showing off. That means, with or without these products, they can make it anyway, because they are those who have the ability to learn by themselves.

⑤In general, the best is the one that suits you most. “Pay-for-knowledge” may be used as a good start for self-growth. But be careful when you make a choice, or your dream of success may not come true.

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It’s late autumn in the Arctic Ocean (大西洋). The water is covered with ice. It’s difficult for the white whales to breathe, so they come up to find openings in the ice to get enough air. As the winter is coming, they know it’s time to leave.

A group of about a hundred white whales swim south toward the Bering Sea. Halfway through their journey, their enemy, an orca (虎鲸) is swimming toward the white whales. With the help of large ice floes (浮冰), the white whales swim faster than the orca. This gives the white whales time to swim away.

After a few more days of swimming, they arrive at the Bering Sea. The white whales will rest, hunt, and play here until April, then they’ll swim back to the Arctic Ocean.