What subject did Fred stay up all night preparing for?

W: Gosh! Fred, another cup of coffee?
M: Yeah ! Well, I stayed up all night preparing for my history exam. I couldn’t keep my eyes open in my last class. I’m having this coffee so I can stay awake this afternoon.
W: Don’t you know that drinking too much coffee is harmful?
M: What do you mean by harmful?
W: Well, f6r one thing it may cause heart disease.
M: No.  Most of the research about the link between coffee and the heart disease is inconclusive.
W: But coffee has caffeine which is addictive.
M: You can’t become addicted to caffeine like other drugs.
W: Yes, you can. Don’t you know that people who are deprived of caffeine suffer with draw symptoms, headaches?
M: One cure for headaches, oddly enough, is caffeine. Haven’t you ever noticed that many over-the-counter headache remedies use caffeine as one of their ingredients? Besides, coffee helps me work faster.
W: Studies have shown that coffee makes you work faster but not necessarily better. You may finish your exam in a shorter period of time but you won’t have fewer errors.
M: You know, that soda you are drinking has caffeine in it too.
W: But 12 ounces of soda has only half the caffeine of a 5 ounces cup of coffee. And a cup of tea has less than that.
M: But I like the taste of coffee. Besides I want something that will keep me alert in class.
W: You could drink decaf.  Decaffeinated coffee doesn’t have as much flavor or body as regular coffee.