Consumer Surplus Loss from Banning Imports Steps:

• In free trade, price is Pw (world price), quantity demanded is Qd (point E1 on demand curve).
• Banning trade raises price to autarky level Pa (point P), reducing quantity to Qa (point Y).
• Consumer surplus with trade is the area above Pw up to demand curve to Qd.
• Loss is the area between demand curve from Qa to Qd and down to Pw, equaling trapezoid PYE1.

Why B is correct:

• PYE1 is the exact area of foregone consumer surplus, per the definition of consumer surplus as integral under demand curve above price.

Why the others are wrong:

• A: PZE1 includes producer surplus gain, not pure consumer loss.
• C: YE2 measures deadweight loss triangle, not total consumer surplus change.
• D: ZYE2 combines unrelated areas like tariff revenue, irrelevant to trade ban.

Final answer: B