A.By removing the bottom of the basket.听力原文: Today, we are going to talk about a special way some plants respond to being invaded by pests. The plants react by emitting a chemical signal, which acts like a call for help. Let's take corn plants for example. Sometimes, caterpillars chew on the corn leaves. When the caterpillar saliva mixes with the chew portion of a leave, the plant releases a chemical scream that attracts wasps. The wasps respond to the signal by flying to the chewed on leave, and laying their eggs on the caterpillars. The caterpillars die in the next few days as the wasp offspring nourish themselves by feeding of them. Thus the corn plant prevents all its leaves from being eaten by the caterpillars. This chemical scream is specific. It's only released after the plant has detected the caterpillar saliva. A plant that is cut by in the other means does not give off the same signal, nor doesn't undamaged plants. This also explains how a wasp can find a caterpillar in a huge field of corn. Soybean, cotton and probably many other plants use similar type of defense against pests. By enhancing this natural response in plants, researchers might reduce, some day even eliminate, the need for chemical pesticide, which can cause ecological damage. For example, scientists might breed plants for this screaming trait, or they might transplant specific genes to increase the release of the chemical signals.听力原文: One winter day in 1891, a class at the training school in Massachusetts, USA, went into the gym for their daily exercises. Since the football season had ended, most of the young man felt they were in for a boring time. But their teacher James Nasmyth had other ideas. He had been working for a long time on a new game that would have the excitement of American football. Nasmyth showed the men a basket he had hung at each end of the gym and explained that they were going to use around European football At first, everybody try to throw ball into the basket no matter where he was standing .Pass ! Pass! Nasmyth kept shouting, blowing his whistle to stop the excited players. Slowly, they began to understand what was wanted of them. The problem with the new game, which was soon called basketball, was getting the ball out of the basket. They used ordinary fruit baskets with bottoms, and the ball, of course, stayed inside. At first, someone had to clime up every time a basket was scored. It was several years before someone came up with the idea of removing the bottom of the basket and letting the ball fall through. There have been many changes in the rules since then and basketball has become one of the world's most popular sports.。