a.) That's very difficult. b.) You've already seen Mr. Chat. (You have already been to see this person) c.) That is unrelated. (It has nothing to do [with something]) a.'s choice of words are somewhat old-fashioned, particularly "tremendously" coupled with "ambitious." Ambitions, or to be ambitious, means a strong will to do something, usually something challenging. "Tremendous ambitions" are exceptionally challenging, and the way it's worded makes it seem that the challenge is not worth the reward. b.'s choice is like a's. It's archaic and hardly used, except in movies depicting older times (like Sherlock Holmes) c. is incomplete. We need to know what "it" refers to, and what the rest of the sentence says. For example, "Doing your chores [has nothing to do] with my decision: you got in a fight, and I'm going to punish you." Alternatively, "I won't go out because I'm lazy? [It's got nothing to do] with that, I think it's just too cold!"