Final answer:
Childcare costs are the primary reason that many single mothers living in poverty do not work outside the home, as these costs can negate the financial benefits of working.
Step-by-step explanation:
The primary reason that many of the 42% of single mothers who live in poverty with their children do not work outside the home is C. Childcare costs. The poverty trap can make the economic gains from working minimal due to additional expenses required for work, such as clothing, transportation, and especially childcare, which can be prohibitively expensive. This financial dynamic also prevents these mothers from gaining valuable job experience and networking, further compromising their future job prospects and trapping them in a cycle of poverty.