参考答案：听力是我们最常做的一件事。然而，听力并不容易。首先，我们被噪音包围着：人们的讲话和叫喊，往来的车马声或者是头上的飞机轰鸣。这些噪音使听力颇具挑战/变得很困难。其次，我们即使在听，也常常似乎记不住内容当一个人结束其十分钟的讲话时，一般听者已经忘记了一半。48小时内，另外的50%也会被忘记。换句话说，我们很快就忘记几乎所有我们所听到的。

解析：
Listening is one of the things we do most. Yet listening isn’t easy. First, we are surrounded by noise—people talking or shouting, the sound of traffic or the roar of airplanes overhead—which makes any listening job a challenge. Second, we often don’t seem to remember even when we do listen. By the time a speaker has finished a ten-minute speech, the average person has already forgotten half of what was said. Within forty-eight hours, another 50 percent has been forgotten. In other words, we quickly forget nearly all of what we hear.