Research on animal intelligence always makes me wonder just how smart humans are.1 the fruit-fly experiments described in Carl Zimmer's piece in the Science Times on Tuesday.Fruit flies who were taught to be smarter than the average fruit fly 2 to live shorter lives.This suggests that 3 bulbs burn longer,that there is an 4 in not being too terrifically bright.Intelligence,it 5 out,is a high-priced option.It takes more upkeep,burns more fuel and is slow 6 the starting line because it depends on learning—a gradual 7—instead of instinct.Plenty of other species are able to learn,and one of the things they've apparently learned is when to 8.Is there an adaptive value to 9 intelligence?That's the question behind this new research.I like it.Instead of casting a wistful glance 10 at all the species we've left in the dust I.Q.-wise,it implicitly asks what the real 11 of our own intelligence might be.This is 12 the mind of every animal I've ever met.Research on animal intelligence also makes me wonder what experiments animals would 13 on humans if they had the chance.Every cat with an owner,14,is running a small-scale study in operant conditioning.we believe that 15 animals ran the labs,they would test us to 16 the limits of our patience,our faithfulness,our memory for terrain.They would try to decide what intelligence in humans is really 17,not merely how much of it there is.18,they would hope to study a 19 question:Are humans actually aware of the world they live in?20 the results are inconclusive.5选？
该空所在句意为：，智力是高成本的选择。显然这是对上文试验结果的总结。表示对结果的说明只有C，故答案为C。A项的主语应该是人，B项一般不会出现在段首，D项词义显然不合语境，均可排除。
