B: benefit: 5000
Cost: 1000 (opp cost), he needs to buy first class ticket: 2000,
Net benefit: 2000
A: benefit: 5000
Cost: if he buys first class ticket: 2000,
if he buys second class ticekt: 1500, and the loss of unable to use computer on plane: 500,
Net benefit: 3000
C: benefit: 5000, and the opptunity benefit: 1000
Cost: first class ticket: 2000
Net benefit: 4000
Choose C