Hi Serhat, In your sentences, "in front of", "beside" and "behind" are prepositions. Prepositions are used before a noun, pronoun or a noun phrase to show their relationship (such as position) with other words in the sentence. Therefore, your sentences should be: I am behind (prep) you (pronoun). The car is beside (prep) the three [boys] (noun phrase). He is *in front of (prep) you (pronoun). * "of" is part of the entire preposition "in front of". I hope this helps.

Good question. I'll try to answer, but I'm not sure. I'm behind. The car is besides the tree. I'm in front of you.

behind you

I'm behind you.