I, O, U.
注：I，O，U三個(gè)元音組成單詞IOU，意思是“借據(jù)”（由I owe you 的讀音縮略轉(zhuǎn)義而成）。
更多英語(yǔ)謎語(yǔ)
What animal took the most luggage into the Ark and what animal took the least?
What are the largest ants in the world?
What can have hundreds of limbs but can't walk？
What breed of dog has no tail?