Final answer:
Investing in a bond fund is the best option for the 75-year-old client who wants to maintain a balance between income and safety of principal for his retirement fund.
Step-by-step explanation:
The best fund that is likely to meet the 75-year-old client's requirement of high income and safety of principal for his retirement fund is b) Bond fund.
Investing in a bond fund is a safer option as compared to stocks or technology sector funds. Bonds provide a fixed income stream through regular interest payments and have a lower risk of loss of principal.
Additionally, bonds are less volatile than stocks and technology sector funds, which makes them more suitable for a retiree who wants to maintain a balance between income and safety of principal.