(山东省潍坊市高三教学质量检测)—Mum ! Jack has broken my toy!

--        Accidents will happen.

A．What is the matter?

B．Doesn't matter.

C．No trouble at all.

D．Why not?

对于一组给定权值所构造的霍夫曼树的形状有可能不同，它们的带权外部路径长度______。