Final answer:
During Road March, CM1 must open the exhaust valve on the generator to allow for cool down, as part of the exhaust stroke process in a four-stroke internal combustion engine.
Step-by-step explanation:
In the case of cooling down a generator during a Road March, CM1 must open the exhaust valve. The process of cooling down a generator involves allowing the hot gases produced during combustion to exit the engine, which is facilitated by opening the exhaust valve. This act is part of the exhaust stroke in a four-stroke internal combustion engine, where the hot gases are expelled to prepare the engine for the next cycle. The constant-volume exhaust phase and the subsequent isobaric compression mentioned in the references are both involved in this exhaust process, ensuring all remaining combustion products are expelled from the engine.