3人の泥棒(2)

There was a burglary in the jewelry store again on Monday.
Three suspects: Ann, Betty, and Cathy were caught and questioned.

Ann  said: Betty did not steal.
Betty said: That is true.
Cathy said: Ann is innocent.

Later on the police found out the thief did tell the truth.
However, at least, one of them was lying. Who was the thief this time?

3人の金髪美女

次の英文の最後の( )に適切な1語を埋めて、この「ジョーク」を完成させてください。

Three blondes are celebrating their success in a pub.
The bartender asks them: “Girls, what’s the reason for the celebration?”
One of the blondes responds: “Well, we just finished this puzzle and it took us only a month, while the box indicated: 3 to 6 ( )!”…

なお、解答では ( ) に入れる語を記載するとともに、オチのおもしろさを簡潔に説明してください。(説明の方は、もちろん日本語で結構です)