Why should we never ask balloons for advice?

谜题：Why should we never ask balloons for advice?（为什么我们绝不向汽球征求意见？）
 
 
谜底：They are full of hot air.因为它们里面全是热空气。
 
谜底提示：They are full of hot air.因为它们里面全是热空气。hot air热空气；吹牛，胡说 

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