为什么说“To replicate the payoff at maturity,we could use 1 long call option with K=100 plus 2 short calls with K=120, which represents the loss in value if S>120”? 按照这一段的例子,那个up-and-out call option 股价到了120以上就不值钱了,payoff=0,但是 1 long call optionwith K=100 +2 short calls with K=120 在K=121的时候的payoff是 21-2×1=19>0的啊。。。求教。。。谢谢