Suppose Country a Has a Production Possibilities Frontier Such That $4 x ^ { 2 } + 4 y ^ { 2 } = 500$

Suppose country A has a production possibilities frontier such that $4 x ^ { 2 } + 4 y ^ { 2 } = 500$ and country B has a production possibilities frontier such that $x ^ { 2 } + 4 y ^ { 2 } = 500$ and consumers in each country view x and y as perfect substitutes.Country B will produce

A) only x (= $\sqrt { 500 }$
) and trade for y.
B) only y (= $\sqrt { 125 }$ ) and trade for x.
C) both x (= 20) and y (= 5) and trade x to get y.
D) both x (= 20) and y (= 5) and trade y to get x.