阅读下面短文，从A、B、C、D四个选项中选出最佳选项。

    Almost everybody in America will spend a part of his or her life behind a shopping cart. They will, in a lifetime, push the shopping carts many miles, but few will know—or even think to ask—who it was that invented them.

    Sylvan N. Goldman invented the shopping cart in 1937. At that time he was in the supermarket business. Every day he would see shoppers lugging groceries around in baskets they had to carry.

    One day Goldman suddenly had the idea of putting baskets on wheels. To create the first shopping cart, Goldman used folding chairs. He out one basket on the seat, and he raised the chair by putting wheels under the legs. The wheeled baskets would make shopping much easier for his customers, and would help to attract more business.

On June 4, 1937, Goldman's first carts were ready for use in his market. He was terribly excited on the morning of that day as customers began arriving. He couldn't wait to see them using his invention. However, Goldman was disappointed. Most shoppers gave the carts a long look, but hardly anybody would give them a try. After a while, Goldman decided to ask customers why they weren't using his carts.

    "Don't you think this arm is strong enough to carry a shopping basket?" one shopper replied.

    Goldman wasn't beaten yet. He knew his carts would be a great success if only he could persuade people to give them a try. To this end, Goldman hired a group of people to push carts around his market and pretend they were shopping! Seeing this, the real customers gradually began copying the phony customers.

As Goldman had hoped, the carts were soon attracting larger and larger numbers of customers to his market. Not only did more people come—those who came bought more. With larger, easier-to-handle baskets, customers unconsciously bought a greater number of items than before.

    Today's shopping carts are five times larger than Goldman's original model. Perhaps that's one reason Americans today spend more than five times as much money on food each year as they did before 1937—before the coming of the shopping cart.

    Bioplastic(生物塑料) is a kind of plastic, but it is not the same as normal plastic. Normal plastic is made from chemical materials and takes a very long time to degrade(降解). But bioplastic is good for the environment. It is made by using bacteria(细菌) to process(加工) natural sources like vegetable oils, corn or sugar. It can degrade more easily.

    But there is a problem with bioplastic. The "food" that bacteria eat is what we eat. This means that bacteria are competing against humans for the same resources.

    Now scientists have found a new way to make bioplastic——using two kinds of bacteria and sunlight, according to Newsweek.

    One of the bacteria can use sunlight to produce sugar. The other kind lives in the salty waters of Bolivia. It eats the sugar that the first bacteria produce and then it can produce polymers(聚合物). Polymers are used to create bioplastics. The way the bacteria store polymers is similar as humans store fats.

    The new way to produce bioplastic has many advantages. It is 20 times faster than the normal way we produce bioplastic. Moreover, using these two bacteria saves resources.

    Firstly, producing a lot of bioplastic requires corn and sugar, which are used to feed normal bacteria. And growing corn and sugar needs farmland. But these two bacteria can just use sunlight. The land that is saved can be used to grow food for humans. Besides, this system doesn't need rich land or clean water at all, scientists said to Newsweek.

    The next problem scientists face is that they want to put their lab research into real-world practice. By doing this, bioplastic made with these two bacteria can be widely produced in the future.

    Now there is too much garbage(垃圾) on the earth. Our planet is in danger, so it is urgent(紧迫) to classify(分类) garbage. How should garbage be classified? The following pictures may help you.