(PPC, Comparative Advantage, Circular Flow)
Answer (C) Countries X & Y can engage in mutually advantageous trade by exchanging 1 watch for 1 radio.
Answer (D) 10
Opportunity cost,, what is given up - to move from 10 to 20 (A) is a gain of 10.
to move from 90 to 80 (B) is a loss of ten.
Lose 10 units of (B) and gain 10 units of (A)
Answer (A) Households are on the demand side of the product market and the supply side of the resource market.