问题如下：
Which of the following is the best reason for an investor to be concerned with thecomposition of a portfolio?
选项：
A. Risk reduction.
B. Downside risk protection.
C. Avoidance of investment disasters.
解释：
A is correct.
Combining assets into a portfolio should reduce the portfolio’s volatility. The portfolio approach does not necessarily provide downside protection or guarantee that the portfolio always will avoid losses.
这道题是在讲义的哪里呢？risk reduction是指风险下跌，为什么风险下跌还会让投资者关心组合的构成呢？？ 另外，downside risk protection是对风险下跌的保护？？怎么翻译，怎么理解这个选项？
