Answer:
a. Dave has a COMPARATIVE ADVANTAGE in the production of sweaters. Â
Explanation:
If both Dave and Caroline produce sweaters and socks. If Dave's opportunity cost of producing 1 sweater is 3 socks, and Caroline's opportunity cost of producing 1 sweater is 5 socks, then  Dave has a COMPARATIVE ADVANTAGE in the production of sweaters.
Comparative advantage can be defined as an economy's ability to produce goods and/or services at a lesser opportunity cost than other countries.
In the end comparative advantage gives a country the ability to sell those goods and services that he could produce at lower opportunity costs; cheaper to other countries.
This definition adequately describes the position  of Dave in relation to caroline, in the given Scenario.