题目内容：

    Picture this: You’re playing soccer with friends. As you kick the ball, you realize the bottom of your foot feels cold and wet. You turn your sneaker up to look at the sole (鞋底). A big crack(裂缝) is letting water from the ground in. When you get home, you throw your ruined sneakers away.

Now imagine another ending to the story. You don’t throw the sneakers away. Instead, you push the two sides of the cracked sole together so they’re touching. You leave the sneaker in a warm spot. A few hours later, the crack disappears.

Thanks to Qiming Wang, a professor at the University of Southern California, a self-healing (自我修复的) sneaker sole could soon become reality. Wang and his team have invented 3D printable rubber that could fix itself. When it’s exposed to heat, it causes a chemical reaction that bonds its atoms back together. The material could be used to3D print not only sneaker soles, but also toys, bike tires, even satellites.

To 3D print a self-healing object, the first step is to make a model of it on the computer. The model is “divided” into 100 smaller pictures. This first picture is projected onto a thin laver (层) of the rubber, which starts as a liquid. The rubber takes on the shape of the picture, and the light from the projection turns it from liquid to solid. The next picture is projected on another layer of liquid rubber on top of the first one. The final, complete shape is built up layer by layer like this.

Many footwear companies want to buy this technology. First, though, Wang and his team have to try to make the material in different levels of hardness. Wang thinks it will take two or three years for their material to show up in shoes we buy in stores.

One exciting thing about the special rubber is the amount of waste it can reduce, Plus, it can self-heal “more than 10 times”. When it can’t heal anymore, it can be recycled.

1.How does the author introduce the topic?

A.By asking questions for readers to think about.

B.By presenting a possible situation in our life.

C.By telling an interesting story about himself.

D.By comparing different research findings.

2.What is the key to the self-healing process?

A.Proper temperature.

B.Strong light.

C.Enough water.

D.Fresh air.

3.What is Paragraph 4 mainly about?

A.The process of 3D printing a self-healing object.

B.The steps to make the self-healing rubber.

C.The material of self-healing objects.

D.The advantages of 3D printing.

4.What do we know about the special rubber?

A.It has a high price.

B.It is environment-friendly.

C.It has a very short usage period.

D.It is being tried by footwear companies.