Research on animal intelligence always makes us wonder just how smart humans are. (1) the fruit-fly experiments described by Carl Zimmer in the Science Times. 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 a(n) (4) in not being too bright.
Intelligence, it (5) , 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(n) (7) process — 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. 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 we’ve ever met.
Research on animal intelligence also makes us 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 locations. 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(n) (19) question: Are humans actually aware of the world they live in (20) the results are inconclusive.
10（）
A.upward
B.forward
C.afterward
D.backward
参考答案：D
解析：
本题各选项的意思分别是，A．upward(向上地)；B．forward(向前地)；C．afterward(然后)；D．backward(向后地)。此空白后面at的宾语为“all the species we’ve left...”，句中修饰species的定语从句作者用了现在完成时，说明动作发生在过去。所以可知前半句作者想表达的意思是“不是去回顾……”，所以选项A，B排除。cast a glance backward at...符合题意。选项D正确。