Final answer:
Considering the cost of living alone, Hillary's family should choose to relocate to Phoenix, as it generally has a lower cost of living than the California cities listed. Option number b is correct.
Step-by-step explanation:
Based on the cost of living alone, the city that Hillary's family should choose to live in is Phoenix. The question asks us to focus solely on the cost of living to make this decision.
While it doesn't provide specific cost of living data for each city listed, it is commonly known that, of the given options, Phoenix generally has a lower cost of living in comparison to California cities like Oakland, San Diego, and Santa Fe. Therefore, Hillary's family should consider relocating to Phoenix to save money.