Is this sentence grammatically correct,and why?

Question

"It must have been about three months ago."
The context is:
How long have they been bothering you?
Er. Well, it must have been about three months ago.


Does tense disagreement exist in this sentence?

Answer 1

The tense is consistently in the past.
The problem is that the question references a duration of time and the answer references a starting point in time.

How long have they been bothering you?
-->They began bothering me about three months ago.
or
-->They have been bothering me for three months.
or
-->Well, it must have began about three months ago.
~

Answer 2

Your sentence is correct by itself. Present perfect works when specific time isn't mentioned, or when talking about a duration of time (especially with for, as it "I have been here for a year").

However, if you want to answer the question, "How long have they been bothering you?", your sentence isn't correct.

You must say something like "They have been bothering me for about three months." OR "It started about three months ago." The first sentence is preferable.

A good rule when confused about which tense to use in a response, is to use the same tense in the question itself.

Answer 3

no the tense (time sense) of the answer doesn't correspond to the question. The question implies an ongoing action that has continued from some point in the past until the present, whereas your answer indicates a specific point in time.

You could either say "well, it started about three months ago" (implying it is still going on), or "it has been about three months now", stating explicitly that the action has continued since three months ago until the present.

Answer 4

The answer should technically be, 'It must be for about three months now.' Because, 'It must have been about three months ago,' answers the question, 'How long ago did they start bothering you?'