The correct answer is C) open the exhaust valves and operate the unit injectors. The rocker arms in a diesel engine serve to convert the rotational motion of the camshaft into the reciprocating motion needed to open and close the engine's intake and exhaust valves. They also actuate the unit injectors, which are responsible for injecting fuel into the engine's cylinders. The other answer choices are incorrect because: A) rocker arms do not directly convert rotational energy to pressure, B) the rocker arms do not operate the starting valves, and D) while the rocker arms do open the intake and exhaust valves, they also have the additional function of operating the unit injectors.