What is dark but made by light?
m o b h l r k d w o n h g e j q a p f i d c s s
knee ------------ light
（猜一个英文词组）
What can be measured but has no length, width or thickness?
This is as light as a feather, yet no man can hold it for long. What is it?(six letters)
What has teeth but cannot eat?
city light有两个不同的玻璃杯（两个杯子都接近圆柱体），两个都装有一定量的水，A杯的水位比B杯高五厘米。A杯的底部沉没着一个石块，当石块被取出并放入B沉没后，B杯水位上升了五厘米，并且比这时A杯的水位还高十厘米。则得知A杯与B杯的底面积之比为多少？
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