NO.PZ2018122701000090
问题如下：
Compared to at-the-money currency options, out-of-the-money currency options exhibit which of the following volatility traits?
选项：
A.Lower implied volatility
B.A frown
C.A smirk
D.Higher implied volatility
解释：
D is correct.
考点Volatility Smile
解析Away-from-the-money currency options have greater implied volatility than at-the-money currency options, this pattern in a volatility smile.
请问volatility frown是怎样的，适用在哪里
