答案是 unless
用but的时候.一般情况下,but后面的句子根前面有某种程度上的相反
ex:I want to go home,but I can't.
ex:The shoes are Nike brand,but they are fake
ex:This dress is fancy,but it doesn't fit me
unless就像是“除非” 需要除非..后面的句子让句子成立
ex:sports shoes were not shoes unless they were Nike or Reebok
－nike和reebok牌子的鞋子才算是运动鞋,其他根本就不算
－运动鞋根本就不能说是鞋子,“除非”它们是nike或者reebok的牌子
我也解释不好...希望你能感觉的出不同哈``