One August many summers ago, I was fishing down a small stream. I did not know when the two sparrows discovered me. In the bush beside me, they were deeply upset, spreading their wings, repeating over and over a rough single note.

When I stopped fishing, they flew to another bush upstream. I thought that perhaps they had new babies somewhere nearby and wanted to lead me away from them, but as I had no intention of harming them, I continued my fishing.

Immediately the two sparrows came back, fluttering before my face. I stopped again to watch them. Once more they flew to a bush upstream, but the minute I faced downstream again, they were back around my head. Not until then did it come to me that maybe they wanted me to go with them rather than lead me from something.

As soon as I started going in their direction, they fluttered on, much less noisily now. I followed them for perhaps a hundred feet until they came to rest in another bush. I looked where they were looking.

There, its tiny leg caught in a crack of a tree stem, hung a baby bird. It hung totally lifeless. I went up, carefully got the little body out and held it for several minutes cupped in my hands. Finally its eyes opened and the stretched leg moved. Both the sparrows had already come close to me. They had obviously no fear of me. I put the baby bird on a branch near its parents and released it only when I saw it take hold of the branch.

I went back to my fishing, but nothing that happened during the rest of the day was as exciting as my meeting with the sparrows. Few things that have happened to me have moved me more since then.

You’ve got to get an early start tomorrow, but you’re not sleepy yet. Blame your brain, at least in part. Yet that same brain is still under construction. And much of that important work takes place while you sleep. Here’s what’s happening and why it matters.

Today’s lifestyle is one reason for late bedtimes. Many teens don’t finish with after-school activities, part-time jobs, dinner, and homework until 10 p.m. or later. Add in some time for relaxing, especially time for screens, and bedtime may not roll around until 11 p.m. or nearly midnight. In response, the brain cuts back melatonin（褪黑素）, a hormone that promotes sleep. Even without modern technology, though, teens change their daily cycle for sleeping, waking, and various other activities.

The rest of the world doesn’t change, however. So most teens must head to school before they’ve gotten the 8.5 to 9. 5 hours of sleep recommended by the American Academy of Pediatrics. And that’s a serious public health problem. For one thing, lack of sleep makes it harder to pay attention. When studies compared teens who had earlier and later school start times, they found that those who had more time to sleep did better in class. They also suffered fewer accidents in sports, driving, and other activities. Lack of sleep could also hurt mental health. Studies have found an inverse correlation（负相关）between teens’ amount of sleep and depression and other mental illnesses. As sleep time went down, the risks for the mental illnesses went up. Beyond that, teens lacking in sleep report more relationship problems and feelings of inadequacy.

Lots of issues remain for sleep researchers to explore. For now, though, studies are clear：Teens’ brains need sleep.

The second little pig was unlucky. He built his house from sticks. It was blown away by a wolf, which quickly ate him up. His brother, by contrast, built a wolf-proof house from bricks. The fairy tale could have been written by a salesman for the construction industry, which strongly favours brick, concrete and steel. However, in the real world it would help reduce pollution and slow global warming if more builders copied the wood-loving second pig.

In 2015 world leaders meeting in Paris agreed to move towards zero greenhouse-gas emissions（排放）in the second half of this century. That is a tall order, and the building industry makes it even taller. Cement-making alone produces 6% of the world’s carbon emissions. Steel, half of which goes into buildings, accounts for another 8%. If you count all of the energy that goes into lighting, heating and cooling homes and offices, the world’s buildings start to look like a serious environmental problem.

Governments in the rich world are now trying to promote greener behavior by requiring developers to build new projects to “zero carbon” standards（标准）. From January 1st 2019 all new public buildings in the European Union must be built to “nearly zero-energy” standards. All other types of buildings will follow in January 2021. Governments in eight further countries are being advised to apply the similar standards.

These standards are less green than they seem. Wind turbines and solar panels on top of buildings look good but are much less productive than wind and solar farms. And the standards only count the emissions from running a building, not those let out when it was made. Those are thought to account for between 30% and 60% of the total over a structure’s lifetime.

At some point in our life, it is likely that everyone will be required to speak to a small or large audience.     11     Apart from this, the need for public speaking can arise in our day-to-day life, be it speaking at a family event or maybe speaking at a debating competition or for a class assignment.

    12     It will help you gain preference over others in a competitive environment. Public speaking also involves good communication and persuasion skills which are highly valued in all areas. Improving your public speaking skills can strengthen your self-confidence. You can put your points forward clearly and quickly, and inform, motivate and win over an audience. Leadership skills are also greatly reflected in a good public speaker.

Often people are afraid of speaking in public. We think that the audience judges us by the way we speak, which is why public speaking leaves a person anxious and nervous.     13    

First, you need to be clear about what you want to speak about and what points you want to focus on.     14     Also, many videos by great speakers can be found online. Watch them and you will notice their skills, ways of speaking and what makes them good speakers.     15     Make sure to practise in front of the mirror. It will help you to focus on your hand movements and you can examine yourself. Through these techniques and practice, you can master the art of public speaking even though it looks tough in the beginning.