Rover: I mean that, in a sentence this noun "people" is plural (so you say "people are" and never "people is"), perhaps you do not know, but in other languages it is singular and when you add a verb it works like "he/she" and not like "them". For instance, this a very common mistake when spanish people learn english.
Raymott: Thanks for your explanation; only one more thing: Can you say "a group of people" or you are better using "a group of persons"? I have used a translator and it shows me the first option, but I don't believe on these translators too much...