Why can't I use order in find method?

In script/console

Storage.find(:all , :conditions => "item_id=1" , order => "expire_date DESC")

I get

NameError: undefined local variable or method `order' for #<Object:0xb7761954>
    from (开发者_运维问答irb):5

But it works when I use

Storage.find(:all , :conditions => "item_id=1")

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order should be a symbol, :order => "expire_date DESC"