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　　【听力问题】

　　What should be the common rule of stuffing into your pack?

　　a. The size and strength of your body.

　　b. The weight is no more than 20% of your body weight.

　　c. The size of your thumb.

　　【原句再现】

　　How much should you stuff into your pack? That depends on your size and strength, but the rule of thumb is not to exceed 20% of your body weight.

　　究竟背包要装多少东西才恰当？这依个人的身材和力量而定，但一般的标准是不超过体重的20%。

　　【短语解析】

　　rule of thumb, 单凭经验的方法 。

　　补充短语：Tom T-, (童话里的)“大拇指,侏儒,矮子; turn up [down] the thumbs, 表示赞成[反对]。