Which of the following wrenches should NOT be used while working on a gas turbine?

Correct Answer: Option A — Adjustable wrench.

Adjustable wrenches are prohibited due to their tendency to slip and damage precision fasteners. In high-performance gas turbine environments, foreign object damage (FOD) is a critical concern; loose-fitting tools can mar bolt heads, creating stress risers or metal shavings that could be ingested, leading to catastrophic engine failure.