Fromoldtimes，crows（乌鸦）havebeenfamousfortheircleverness...

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From old times，crows（乌鸦）have been famous for their cleverness. They use tools，work out problems，and even enjoy playing. Scientists have studied carefully how crows go about these activities.

To make tools，crows cut off leaves with their “mouths”，shape them，and use them to look for bugs(虫子）in wood or plants. Just as a carpenter carries his tools with him，a crow will carry its tool around. When the leaf isn't needed for the moment，the bird stores the tool at its feet or somewhere else.

To test wild crows’abilities to work out problems，scientists placed food outdoors in covered bowls. They watched with interest as the birds smartly opened the bowls to get the food. Scientists also found out that crows can make use of the traffic. For example，crows would drop a nut on the road and wait for a car to run over the nut to break it.

Besides，crows seem to enjoy playing. Young crows will carry a stick or nut into the air，drop it，and fly to catch the object as it falls.

So just how smart are crows? Perhaps a crow will never do tricks as a dog scientists agree that there's a lot going on in the brain of a clever crow.

30. We learn from paragraph 2 that a crow may store the at its feet or somewhere else.

A. leaf B. mouth C. wood D. bowl

31. Scientists placed food outdoors in covered bowls in order to test .

A. Whether crows make tools

B. Whether crows enjoy playing

C. How much crows like the food

D. How crows work out problems

32. The writer uses a(n) to show how crows make use of the traffic.

A. survey B. guess C. example D. experiment

33. This passage mainly discusses the of crows.