【英文原文】
The ability of the Kangaroo
The zoo built a special eight-foot-high enclosure for its newly acquired kangaroo, but the next morning the animal was found hopping around outside. The height of the fence was increased to 15 feet, but the kangaroo got out again. Exasperated, the zoo director had the height increased to 30 feet, but the kangaroo still escaped. A giraffe asked the kangaroo, "How high do you think they'll build the fence?"
"I don't know, " said the kangaroo. "Maybe a thousand feet if they keep leaving the gate unlocked.