The additional benefit of producing one more roast beef sandwich at a local deli is $2. The additional cost of producing one more roast beef sandwich is $3. To improve allocative efficiency:

producers should produce at least one more roast beef sandwich because MB > MC.
producers should produce at least one more roast beef sandwich because MC > MB.
producers should not produce one more roast beef sandwich because MB > MC.
producers should not produce one more roast beef sandwich because MC > MB.