The world is not hungry, but it is thirsty. It seems strange that nearly 3/4 of the earth is covered with water while we say we are short of (短缺) water. Why? Because about 97% of water on the earth is sea water which we can’t drink or use for watering plants directly. Man can only use the 3% of the water that comes from rivers and lakes. And we can’t even use all of that, because some of it has been polluted.

Now more water is needed. The problem is: Can we avoid a serious water shortage (短缺) later on? Firstly, we should all learn how to save water. Secondly, we should find out the ways to reuse it. Scientists have always been making study in this field. Today, in most large cities, water is used only once and then runs to the sea or rivers. But it can be used again. Even if every large city reused its water, still there would not be enough. What could people turn to next?

The sea seems to have the best answer. There is a lot of water in the sea. All that needs to be done is to get the salt (盐) out of the sea water. This is expensive, but it’s already in use in many parts of the world. Scientists are trying to find a cheaper way to do it. So you see, if we can find a way out, we won’t be in danger of drying up.

For many people, life is much better now than before. People have more ways to create wealth. They have more spare time to enjoy themselves. 1. ________ But there were only candles in the past. Medicine and diet are improving, and people are getting healthier and living longer. 2. ________ They can have a good education like men. And they can go to work even after getting married. But communication is changing fastest of all. Today, with the Internet, people can communicate easily with their friends all over the world. But in the past, people wrote to each other, so many postmen often worked very long hours a day outside in the winter cold or in the summer heat.

3. ________ Although transport and travel are easier today—more people drive cars instead of riding bikes, they seldom take exercise every day. 4. ________ Increasing traffic makes the roads more crowded than ever, and the air is badly polluted. We must work harder to reduce pollution. Let’s take action!

Anna Du was walking along the beach when she noticed plastics there. She reached down to pick them up, and quickly realized there were many more tiny pieces than she could deal with. It seemed impossible to clean them all up.

Du, 12 years old at the time, tried to solve the problem like any good scientist—first, by doing a little research. That’s how she learned that 8 million tons of plastics end up in the oceans every year.

Then she got to work building something that could help solve the problem: a remote-operated vehicle (遥控潜水器), or ROV. Her ROV can move through water and find plastics on the ocean floor.

The actually cool part of Du’s ROV is the detection (探测) system. She uses a camera along with three different kinds of light to find the plastics. She also uses visible (可见的) light to find unnatural colors that might make the plastics stand out.

“She has a very good engineering sense to break down a problem like this and then go after it,” says engineer Casey Machado. “It sounds simple, but it’s a level of thinking that’s really amazing.”

Du started attending public events and workshops at a university when she was five years old, and so she picked up the engineering skills necessary to build her ROV. She says actually getting her ROV to move through water well was not easy. She failed many times, but she never gave up trying and testing.

When asked about future plans, she mentions wanting to address the effects of climate (气候) change. “I think there are a lot of problems that could be solved with new inventions,” says Du.

Du thanks her parents, who for years have taken her to student outreach activities, for supporting her interest in science, technology, engineering and math (STEM). She says she has been able to meet students and scientists there.

“I know I want to be an engineer because I like building things to help solve world problems,” says Du. “But I’m not sure what kind of engineer I want to be yet.”