According to Gregory Mankiw, a US teacher and economist, this example would demonstrate the economic principle of "the significance of opportunity cost in decision making". Martina had to give up going to restaurants in order to continue travelling by taxi. She probably compared the cost and benefits of packing lunch vs going to a restaurant before taking the final decision.
I believe the answer could be C
What even is the question
Korean War and the Cuban Missile Crisis are two separate events. They are, however, connected through their cause (the more general one, not the more direct ones): the Cold war. The Cold war was a high potential of armed conflict between the West and East block, but there was no direct war, only proxy wars (such as the Korean War).