Translation:A lot has been changing in the past years.
"Lots have been changing in the last years" is an accepted answer.
Can any English native speaker explain to me, why it has to be have and not has like in the above example "A lot has been changing..."
My answer "Lots has been changing in the last years" was rejected by DuoLingo.
This sentence raises two important points. Firstly the actual question about the person of the verb. 'Lots have been changing' could be right in certain contexts, e.g. following on from a previous sentence referring to a group of items/people such as: 'The shops round here always used to be independent retailers, but lots have been changing...' However, normally 'Lots have been changing ...' is a sign of a foreign speaker trying to apply a rule. We have in English many common usages which go against the rules, one of which is to consider 'lots' as a singular noun. Extending the discussion about the verb, I would also prefer to say 'much has changed...'. This is far more common in English than the imperfect, and we use it to express gradual change over time.
The other point is 'the last years'. This is just wrong unless qualified as 'the last years of the regime/the century/a person's life'. In English we would say 'in recent years' or 'in the past few years'.
As a native English speaker I think 'Lots has been changing' is in fact correct, not 'have been' changing if you wish the 'lots' to refer to 'many things'. Here the 'lots' in English, although plural is rather like 'a gente' or 'o povo' in portuguese and so is treated as 3rd person singular. If you use 'lots have been changing' then this, to an English speaker, is more likely to refer to lots in an auction (things that are available for sale). I believe Duolingo probably have this one wrong
The use of a singular or plural verb depends on the subject.
A lot of money/Lots of money is spent on smartphones.
A lot of people/Lots of people study ESL.