单选题 Experienced baseball fielders can tell how far a ball is going to travel just by listening to the crack of the bat. If they didn't, they wouldn't stand a chance of catching it, claims a physicist in New York. "When a baseball is hit straight at an outfielder, he cannot quickly judge the angle of the scent and the distance the ball will travel." says Robert Adair, a physicist at Yale University. If he relied purely upon visual information, the fielder would have to wait for about one-and-a-half seconds before he could tell accurately if the pitcher hit the ball long or short. By this time the ball may have traveled too far for him to reach it in time. To stand a fighting chance of catching it, according to Adair, fielders must listen to the sound the ball hitting the bat to judge how far it will travel. There is anecdotal evidence to support this, he says. A former centre fielder told Adair: "If I heard a crack 1 ran out, if I heard a clunk, I ran in." To test his hypothesis, Adair calculated how quickly a fielder could change direction if he had misjudged whether the ball was going long or short. The difference between the "crack" and "clunk" can be explained by how well the batter has hit the ball, and could mean a difference in running distance of as much as 30 metres, he told delegates at a meeting of the Acoustical Society of America in Chicago last week. Scientists already knew that to hit a ball long the batter must strike it somewhere near the vibrational node of the bat, known as the sweet spot. Balls hit on the sweet spot generate fewer energy-sapping vibrations in the bat, allowing greater energy transfer to the ball. Conversely, mishit balls make the bat vibrate strongly and so do not travel as far. Adair is quick to point out that this only applies to wooden bats, which are used in major league baseball. Aluminum bats, on the other hand, tend to produce a fairly uniform "ping" sound regardless of where you hit them.

单选题 According to Robert Adair, why can't an outfielder rely purely on visual information?

【正确答案】 A

【答案解析】解析：根据文章第二段最后两句“If he relied purely upon visual information…．traveled too far for himto reach it in time．”可知，如果仅凭视觉信息，外场员就必须要等待1．5秒才能准确判断出投手是长击还是短击。在这个时候，球已经飞行了太远，外场员已经不能及时抓住它了。据此判断，答案是A。

单选题 From paragraph 3 we can infer that a "crack" may mean______.

【正确答案】 A

【答案解析】解析：根据文章第三段最后一句“A former centre fielder told Adair：‘If I heard a crack 1 ran out，if I hearda clunk，I ran in．’”可知，一位退役的主力外场员告诉亚戴尔：“听到开击声我就向外跑，听到撞击声我就向里跑。”所以，开击声可能意味着长球。据此判断，答案是A。

单选题 If the bat vibrates very little,______.

【正确答案】 C

【答案解析】解析：根据文章第五段“Scientists already knew that to hit a ball long the batter must…Conversely,mishitballs make the bat vibrate strongly and so do not travel as far．”可知，科学家们已经知道，发长击球的时候，击球手必须击打在球棒的共振点处，亦即最佳击球位置。击打在最佳击球位置，在球棒上产生的减少能量的共振的几率就小，传给球的能量就大。与此相反，误击球会在球棒上产生强烈的共振，致使球的飞行距离不远。据此判断，答案是C。