Why was the outcome of the battle of bull run surprising to northners

What is the most likely result of specialization in producing products a and b? a) japan stops producing and using product b. b) the u.s. stops producing and using product a. c) the increased output means the u.s. and japan can trade excess units of products a and b. d) specialization means the u.s. will trade 800,000 units of product b for 60,000 units of product a.