题目是："The higher interest rates are, the easier it is for a bank to create a principal protected note." Explain this statement.
给的解释是：In a principal protected note, the price of a call option has to be greater than the difference between S and PV(S). As interest rates increase, the difference becomes greater. Thus, it is easier to create a principal protected note.
按照老李上课的讲解，
最后是
10000/(1+r)^3+C0<= 10000，构建成本不高于1万，不应该是用这个角度来解释题干：构建成本越低，使得银行越容易去创建PPN。
而本题目的解释是，C0应当大于10000-10000/（1+r）^3，按老李的讲解，应该是小于才对？另外利率上升，差增大，为啥就有利于构建PPN了？
