The correct answer is C. years until retirement. The ability to bear risk is primarily measured by objective factors, such as time horizon. For instance, an investor with a 20-year time horizon has a greater ability to bear risk compared to an investor with a 2-year horizon, all else being equal.

• A (risk attitude) is incorrect because it reflects the investor's willingness to take risk, which is a subjective factor based on psychology and circumstances, not their ability.
• B (self-confidence) is also incorrect as it is associated with the investor's willingness to take risk, not their ability. Psychological factors like self-confidence influence risk attitude, not the objective capacity to bear risk.