Final answer:
The sound advice based on the efficient markets hypothesis is to invest in low-cost index funds.
Step-by-step explanation:
Based on the efficient markets hypothesis, the sound advice is to invest in low-cost index funds. This is because index funds seek to imitate the overall behavior of the stock market, providing a diversified investment with lower risks compared to investing in individual stocks. On the other hand, buying individual stocks based on insider information is illegal and unethical. Timing the market to maximize profits is challenging, as it is difficult to predict future expectations accurately. Investing in high-risk, high-reward assets can be a risky strategy and may not align with the efficient markets hypothesis.