Answer: have the highest rates of return for a given level of risk
Explanation:
When it comes to investment, one must realize that there are investments with varying risks and these risks must be compensated for by the return offered. The return should therefore be based on the risk of the individual investment not a general risk.
This is what efficient portfolios do. They have investments that offer the highest rates of return for the given level of risk that those investments have so that the investor is receiving the highest return possible for their investment.