Question 20 is based on the recording you have just heard.

听力原文

    In 1984, the World Chess Championship was called off abruptly due to the withered frame of a player who was competing for the title. He wasn’t alone in experiencing extreme physical effects of the game. Elite players can reportedly burn up to an absurd six thousand calories in one day.

    Does that mean that thinking harder is a simple route to losing weight? Well, (19) [when the body is at rest, we know that the brain uses up a startling 20% to 25% of the body’s overall energy.] This level of utilization actually makes the brain the most energy-expensive organ in the body, and yet it makes up only 2% of the body’s weight overall.

    So the more we put this organ to work, the more calories we’ll burn? Technically, the answer is yes, for cognitively difficult tasks. What counts as a “difficult” mental task varies between individuals. But generally, it could be described as something that “the brain cannot solve easily using previously learned routines, or tasks that change the conditions continuously”. However, deep thinking will not burn off the calories gained from eating a sugary snack. Because in relation to the brain’s huge overall energy usage, which is devoted to a multitude of tasks, the energy required just to think harder is actually comparatively tiny. (20) [We are unconscious of most of what uses up the brain’s energy—a lot of that activity is unrelated to conscious activities like learning how to sing or play the guitar.]

    (21) [The brain is able to allocate blood and thus energy to particular regions that are being active at that point. But the overall energy availability in the brain is thought to be constant.] So, while there might be significant increases in energy use at localized regions of the brain when we perform difficult cognitive tasks, when it comes to the whole brain’s energy budget overall, these activities don’t significantly alter it.

    So why did the chess champion grow too skinny to compete in his chess competition? The general consensus is that it mostly comes down to stress and reduced food consumption, not mental exhaustion. Keeping your body pumped up for action for long periods of time is very energy-demanding. If you can’t eat as often or as much as you can or would normally, then you might lose weight.

20. What does the speaker say about the consumption of the brain’s energy?（关于大脑消耗的能量，讲话者说了什么？）

解析：A。录音中间提到，我们不知道大脑消耗的大部分能量用在了哪些活动上——其实很多活动都与学唱歌或学弹吉他这类有意识的活动无关。A项与此内容相符，其中has nothing to do with对应录音中的is unrelated to，conscious activities为原词复现，故A项为正确答案。

错项排除：录音中间部分提出了问题：是不是我们越使用大脑，我们消耗的卡路里就越多呢？随后给出答案：当大脑在执行高难度的认知任务时，答案是肯定的。B项干扰性较强，录音中提到cognitively difficult tasks（高难度的认知任务），但录音中只是问消耗的卡路里是不是就越多，并没有特指是大脑消耗的卡路里，故B项错误。录音中提到，我们并不知道大脑能量消耗占比较大的活动都有哪些，所以主动的学习和完成高难度的认知任务所消耗的能量占大脑总能量消耗的比例尚未可知，C、D项与录音内容相悖，故排除。