Your answer is going to be D) or C)
This is a complex sentence it includes a subordinate clause (one that CANNOT stand by itself), and a dependent clause. You can tell this because if I were to walk into a room and say, "When K and C read the same foldable....", you would be waiting to hear the rest, wouldn't you? A compound sentence has two independent clauses joined by a comma and a coordinating conjunction (but, and, for, nor, or, so, yet). A simple sentence is just an independent clause.
Answer:
opportunity costs are the alternative choice in which you could make when making a financial decision while a trade-off is something that you could switch out in order to make a different decision
