It is probably worth noting that while "No, I don't mind at all" is correct, typically native speakers will not respond so formally. Depending on where the person comes from you are likely to hear responses such as: "It's fine" "It's ok" "Not a problem" However, as janee mentioned if someone is busy the response will likely be negative.

Out of the choices you have given the best reply to 'sorry to trouble you' is B) No, I don't mind at all. But actually we would most likely respond with ' Don't worry, it's no trouble at all 'Sorry to trouble' you is often used before making a request. In this case the response would be 'No problem, how can I help you'. You can also say 'sorry to bother you'.

I think the answer is: "Nothing, do not make excuses. Please."

B. No, I don't mind at all.

I would reply : "Don't worry"