Microeconomics questions, please help.

Answer the following in your own words (a couple of sentences is ne). In each of the following situations, explain whether your friend is talking about cost like an economist would. (a) Your friend inherits a farm but he doesn't plant anything on the land. He says to you: "There's no cost to me if I let the farm fall apart since I didn't pay any thing for it." (b) Your friend is doing research and you ask him how it is going. He says: "Well, I've been working on this model for a long time and I just realized that it's wrong. However, I can't change my model because I've spent so much time on it. The cost of starting over is just too high!\" (c) You're having some socially distanced drinks with a friend on Zoom and, as usual, you and your friend are talking about economics. Your friend makes the following strange claim: \"A big company where I live just shut down and there really aren't any jobs there. The cost of me going to university is lower now.\