The correct answer is A) Provide a dirt pocket and strainer ahead of the steam trap on a unit heater return. This is considered a good design practice because it helps protect the steam trap from debris and contaminants that could interfere with its proper functioning. The dirt pocket and strainer act as a filter, catching any sediment or particles before they reach the trap, which can help extend the trap's lifespan and maintain efficient operation of the steam heating system. The other answer choices are not considered best practices - B) requiring all units to have a dirt trap and gate valve is overly complex, C) vertical condensate piping runs are not always necessary, and D) orifice-type bypasses are not typically recommended for steam traps.