Which one of the following can be a major attraction to investing in exchange-traded funds (ETFs) in a retirement account? A) ETFs, unlike mutual funds, can offer numerous diversification choices and investment strategies. B) ETFs provide diversification opportunities because they are available in numerous asset categories including commodities, real estate, and currencies. C) ETFs are always liquid and can easily be sold anytime at net asset value. D) ETFs are generally not tax-efficient so they are often purchased in a sheltered retirement account for tax savings