A city plans to install expensive solar-powered streetlights to reduce energy costs and its carbon footprint. City officials project that this investment will pay for itself within ten years through energy savings. This projection is sound. Which of the following is an assumption on which the city officials' projection relies?
✓ Correct Answer: Option A
For the solar streetlights to generate sufficient energy savings to pay for themselves, the cost of the energy they replace (traditional electricity) must remain high enough to make the savings meaningful.