- There has been a lot of advertisements.
- There have been a lot of advertisements.
Which is right? 1) There has been a lot of advertisements. 2) There have been a lot of advertisements.
Let's substitute many for a lot of:
There have been many advertisements.
Since many is semantically the same as a lot of. It shows how the sentence requires a plural. Many people are misled by "a lot of". That is just an adjective and has no bearing on whether the noun is plural or singular. If the noun is plural, the verb of the impersonal expression (there is, here, in the present perfect form: there have been) has to be plural also.
Now, let's substitute a lot of for many.
There have been a lot of advertisements.
The correct form here is plural.
Normally we determine has/have the pronoun they follow:
- He has one
- We have one
In your example the word in question is not following a pronoun, but consider:
- There is an advertisement
- There are advertisements
In your example, therefore, it should be there have been a lot, because you are referring to many advertisements and "have" is plural whereas "has" is singular.
People can probably argue themselves around in circles as to which is 'right', based on a simple question: is the object (main noun denoted by emphasis) "a lot of advertisements" or "a lot of advertisements". One would be singular, the other plural.
Here's the simple answer, though: native speakers say both versions as given in the question, all the time. Which one is more common probably depends on dialect, but no-one except a pedantic grammarian will pick them up on it, and different pedantic grammarians will probably insist on a different 'right' answer.
There are certainly cases where it is more usually treated as a singular - where you are, say, comparing this lot of advertisements with that lot of advertisements.
As a final note, however, it is worth saying that if you are taking a class where you are learning or demonstrating English, you should try to conform to your teacher's expectations. At least, you should do that if you don't want to make a point and argue with your teacher. Most likely, they expect you to consider advertisements as the main noun of the phrase, and treat it as plural.