The correct answer is C) the steam enters the high pressure unit and then flows through a crossover to the low pressure unit. In a cross-compounded turbine propulsion plant, the steam first enters the high pressure turbine. It then flows through a crossover pipe to the low pressure turbine, where it expands further before being exhausted to the condenser. This sequential flow through the high and low pressure units is the defining characteristic of a cross-compounded arrangement. The other options are incorrect because they do not accurately describe the flow path of the steam in a cross-compounded system. Option A describes a single-compound arrangement, option B describes a parallel flow configuration, and option D describes a triple-expansion arrangement, none of which are correct for a cross-compounded turbine.