单项选择题 一项研究发现，1970年调查的孩子中有70%曾经有过龋齿，而在1985年的调查中，仅有 50%的孩子曾经有过龋齿。研究者们得出结论，在1970年至1985年这段时间内，孩子们中的牙病比率降低了。 如果为真，以下哪项最能削弱研究者们上面得出的结论?（）

单项选择题 张教授：智人是一种早期人种。最近在距今百万年前的智人遗址中发现了烧焦的羚羊骨头碎片的化石。这说明人类在进化的早期就已经知道用火来烧肉了。 李研究员：但是在同样的地方也同时发现了被烧焦的智人骨头碎片的化石。以下哪项最可能是李研究员所要说明的?（）

单项选择题 听力原文： A lot of people in the United States are coffee drinkers. Over the last few years, a trend has been developing to introduce premium specially blended coffees known as gourmet coffees into the American market. Boston seems to have been the birthplace of this trend. In fact, major gourmet coffee merchants from other cities like Seattle and San Francisco came to Boston, where today they engaged in a kind of coffee war with Boston's merchants. They are all competing for a significant share of the gourmet coffee market. Surprisingly, the competition among these leading gourmet coffee businesses will not hurt any of them. Experts predict that the gourmet coffee market in the United States is growing and will continue to grow to the point that gourmet coffee will soon capture a half of what is now a 1.5 million-dollar market and will be an 8 million-dollar market by 1999. Studies have shown that coffee drinkers who convert to gourmet coffee seldom go back to the regular brands found in supermarkets. As a result, these brands will be the real losers in the gourmet coffee competition.What is the main topic of the news story?A．The coffee market in Boston.B．The role of supermarkets in the coffee business.C．A new trend in the United States.D．The advertising of a new product.