The correct answer is C) single-pass heat exchanger. A main condenser that utilizes a scoop for the circulation of seawater must be constructed as a single-pass heat exchanger. This is because the seawater enters the condenser through the scoop, flows across the condenser tubes in a single pass, and then exits the condenser. This is in contrast to a parallel flow or counter-flow heat exchanger, which would require the seawater to make multiple passes through the condenser. The other options, parallel flow (A), counter-flow (B), and two-pass (D) heat exchangers, are not the correct configurations for a main condenser with a seawater scoop, as they do not match the single-pass flow pattern required for this type of system.