How many distilling units are typically located in each Main Machinery Room (MMR)?

In most naval ships, each Main Machinery Room (MMR) typically houses two distilling units. The primary function of these distilling units is to convert seawater into fresh water through a process known as desalination. By having two units in each MMR, redundancy and reliability are ensured; if one unit were to go offline for maintenance or repairs, the second unit would continue to supply fresh water to meet the ship's operational needs.

This setup is particularly important for sustaining long missions at sea, where access to fresh water is limited. The presence of two units allows for effective water production during various operational conditions, maintaining safety and readiness. Moreover, this number is optimal for balancing the operational demands with the space available in the MMR, making B the most fitting answer.