The correct answer is C) Pintle. The pintle-type fuel nozzle requires the least maintenance compared to the other options. This is because the pintle design is relatively simple, with fewer moving parts and less complexity. The pintle nozzle uses a single, tapered needle-like pintle to control the fuel flow, which results in less wear and tear over time compared to more intricate nozzle designs. In contrast, the other options, such as open, single-hole, and multi-hole nozzles, have more components that can wear out or become clogged, requiring more frequent maintenance and servicing.