$45.$ Which of the following statements regarding retirement trends is correct?

a$.$ The savings rate in the United States has consistently been increasing over the last $30$ years.

b$.$ The spending pattern of most elderly retirees shows an average decline in outflow during the latter part of retirement.

c$.$ Analysis of Social Security shows that only a small percentage of retirees in the United States rely on Social Security benefits as a major part of their retirement sources of income.

d$.$ Historically, the retirement age for citizens of the United States has been increasing as workers life expectancy has been increasing. However, that trend has been reversing over the last ten to fifteen years.