[tabako]

For question 1, C is definitely not correct. You would need something in the question that explicitly stated what kind of production function you were working with for C to be an accurate statement (it may or may not be depending on the production function). And even then, it wouldn't be true due to "the law of opportunity cost." It would be true because of "the law of decreasing marginal utility", which is sometimes stated "as the law of increasing opportunity cost."

I really like E as the correct answer, as I interpret the "law of opportunity cost" as simply stating that whenever you choose to do something with your time or choose to buy something, there is an implicit cost which takes the form of you not being able to do something else with that time or that money.

While it is true that under (normal) circumstances, as the cost of something increases, people will substitute away from that good, it is wrong to call this the the "law of opportunity cost"