"They are my friends playing football in the playground" Is this sentence correct?
In the textbook it is written "I'm in bed, because I'm ill. Looking through the window is my only fun. Look. ______ are my friends playing football in the playgroud."
So, I think that the right answer is "Those", but I am not sure. And is it posible to be "They"? If it isn't, why not? Is it possible to have this construction in the sentence? Like, "He is my boyfriend sitting next to me"?

Question

"They are my friends playing football in the playground" Is this sentence correct?
In the textbook it is written "I'm in bed, because I'm ill. Looking through the window is my only fun. Look. ______ are my friends playing football in the playgroud." 
So, I think that the right answer is "Those", but I am not sure. And is it posible to be "They"? If it isn't, why not? Is it possible to have this construction in the sentence? Like, "He is my boyfriend sitting next to me"?

Answer

Hi Giovana, the word 'Look' suggests that the speaker/writer can see his (or her) friends playing football in the playground, and might be indicating WHERE the friends are, rather than WHO they are.  This means that the right word could also be 'There', as in "There they are, over there! [in the playground]"

Does this make sense to you?

Answer

"Those are my friends ..."  and "This is my boyfriend ..." are the natural versions.  "They" and "He" only work as answers to the questions "Who are they?"  and "Who is he?"