Concept:This question tests the meaning of the common idiom "as dull as ditchwater."Explanation:In this idiom, the word "dull" means boring or uninteresting, not slow-witted or dark-skinned. Ditchwater is still, stale water found in a ditch, and it suggests something lifeless and tedious. So, when someone says a friend is as dull as ditchwater, they mean the friend is extremely boring. Among the given options, the most appropriate interpretation is the one that describes a person who is very uninteresting.Answer:B. extremely boring