You can't predict the twists and turns of your life, and neither you nor anyone else can consistently and reliably forecast the financial markets or the economy - not even Alan Green Span. So how in the world can you figure out how much money you have to put aside to support you in your retirement years? It's like trying to assemble a puzzle when critical pieces are (　A　) and you're not even sure what the final picture should look like. You have little choice, however, (　B　) to try - “particularly the closer you are to retirement,”says a financial planner, “because you have less time to fix it if you get off track.” Planners suggest that you start by coming up with a realistic estimate of your projected expenses for the first year of retirement. Some pre-retirement expenses will drop, of course. [1]The cost of commuting, business apparel, and other work-related items will dwindle. And you might decide to pay off your mortgage, eliminating a significant monthly payment. Some expenses, however, will rise - such as health-care, and perhaps travel and entertainment. “When you run the numbers, add a cushion,” warns a certified financial planner. Getting through [2]that exercise will be difficult enough, but your next assignment will be harder. Now that you know your expenses, you'll have to guess at the rate of return you expect to receive on your retirement nest egg and how many years you think your savings will have to (　C　) . Judging multiple “if then.” variables is difficult even for professionals. Small changes in anticipated expenses, expected annual return, and number of years in retirement can dramatically shrink or balloon the calculated size of [3]the nest egg.