My friend is as dull as ditchwater. This means that my friend is

Analyze the question: This is an idiom question. "As dull as ditchwater" (also "dull as dishwater") is a fixed expression, so you can't work out its meaning from the individual words alone.

Explain the concept: Ditchwater is the stagnant, murky water that collects in a ditch. It is lifeless, unattractive, and uninteresting. When we describe a person or thing as "as dull as ditchwater," we mean it is very boring and lacking in excitement or interest.

Step-by-step solution:

• A. dark in complexion: "Dull" here does not refer to skin color. Wrong.
• B. extremely boring: The idiom stresses a lack of excitement and interest, and "as...as" shows an extreme degree. This fits.
• C. not intelligent: This is a common trap. "Dull" can sometimes mean slow-witted, but the idiom is about being tedious, not about intelligence. Wrong.
• D. not a troublemaker: This has no connection to the idiom. Wrong.

Exam tip: For idiom questions, don't be fooled by the everyday meaning of one word (like "dull" suggesting "not intelligent"). Ask yourself what the whole phrase means. Also remember similar comparisons: "as dry as dust" (boring), "as clear as crystal" (very clear), "as busy as a bee" (very busy). Learn idioms as complete phrases.