Lavatory trap arm feeding a wet-vented water closet
Not quite. The answer is B: Wet venting — its drain shares the same pipe that vents the lavatory upstream
The 2-inch pipe downstream of the lavatory's trap arm is doing double duty in the drawing — it carries the lavatory's waste and also serves as the water closet's vent path, which is the definition of wet venting. There's no separate dry vent pipe running to the water closet itself, which rules out individual venting.
Checked against the 2021 UPC text. Washington's exam is written against the 2015 edition, which we have not read for this section, so confirm it against your 2015 book.
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