根据以下材料，回答下面试题
　　From the goose that laid the golden egg to the race between the tortoise and the hare，Aesop's fables are known for teaching moral lessons rather than literally being true. But a new study says at least one such tale might really have happened.
　　It's the fable about a thirsty crow (乌鸦). The bird comes across a jar with the water level too low for him to reach. The crow raises the water level by dropping stones into the jar. The moral tells:Little by little does the trick,or in other retellings, necessity is the mother of invention.
　　Now,scientists report that some relatives of crows called rooks used the same stone-dropping strategy to get at a floating worm. Results of experiments with three birds were published online by the journal Current Biology.
　　Rooks,like crows, had already been shown to use tools in previous experiments.Christopher Bird of Cambridge University and a colleague exposed the rooks to a 6-inch-tall clear plastic tube containing water, with a worm on its surface. The birds used the stone-dropping trick naturally and appeared to estimate how many stones they would need. They learned quickly that larger stones work better.
　　In an accompanying commentary, Alex Taylor and Russell Gray of the University of Auckland in New Zealand noted that in an earlier experiment, the same birds had dropped a single stone into a tube to get food released at the bottom. So maybe they were just following that strategy again when they saw the tube in the new experiment, the scientists suggested.But Bird's paper argued there's more to it: The rooks dropped multiple stones rather than just one before reaching for the worm, and they reached for it at the top of the tube rather than trying to reach the food at the bottom.
　　The researchers also said Aesop's crow might have actually been a rook,since both kinds of birds were called crows in the past.
　　第26题 What is the main idea of this passage?
　　A.Animals are smarter than we have expected.
　　B.Aesop's fables tell real morals.
　　C.Necessity is the mother of invention.
　　D.Some of Aesop's fables may be true.
　　第27题 Aesop's fables have been popular for such a long timebecause they_____.
　　A.tell us the truth of nature
　　B.tell us interesting stories of animals
　　C.are teachings of life
　　D.are scientific literature
　　第28题 In the experiments, in order to eat the worm floating onthe water surface, the rooks_____.
　　A.found a way to raise the water level
　　B.broke the tube with larger stones
　　C.counted how many stones they would need
　　D.cooperated peacefully
　　第29题 According to Alex Taylor and Russell Gray, it seems thatrooks_____.
　　A.tend to follow the others' strategy
　　B.can remember their former strategy
　　C.can change strategy in different situations
　　D.seldom use the same strategy in experiments
　　第30题 According to the passage, crows and rooks_____.
　　A.are the same kind of birds with different names
　　B.are very different in behavior
　　C.had the same name in the past
　　D.were both used in the experiments

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