The Black-Scholes-Merton (BSM) model is a cornerstone of option pricing, but a core assumption is that the underlying asset's volatility remains constant over the option's life. However, in real option markets, we commonly observe the phenomenon of 'volatility smile' or 'volatility skew'. a) Explain what volatility smile/skew is and discuss its primary causes. b) What are the implications of volatility smile/skew for option traders and risk managers? c) Briefly describe how the Black-Scholes framework is adjusted or extended in practice to account for this phenomenon.

Black-Scholes-Merton (BSM) 模型是期权定价的基石，其核心假设之一是标的资产的波动率在期权生命周期内保持不变。然而，在现实期权市场中，我们普遍观察到“波动率微笑”或“波动率偏斜”现象。 a) 请解释什么是波动率微笑/偏斜，并讨论其出现的主要原因。 b) 波动率微笑/偏斜对期权交易员和风险经理意味着什么？ c) 简要描述实践中如何调整或扩展Black-Scholes框架来解决这一现象。