If an operating bilge pump is developing good vacuum, but is unable to discharge any water, which of the following problems is the most probable cause?

Correct Answer: Option C — The suction strainer is clogged.

A centrifugal pump developing vacuum but failing to discharge indicates a suction-side restriction. If the strainer is clogged, the pump cannot draw sufficient fluid to build discharge pressure, even if the pump casing remains primed and the internal vacuum is high.