Answer :
The right answer is variant a) because it respects the order:
Subject+Verb+ Predicative name + Atribute
Subject+Verb+ Predicative name + Atribute
The answer would be a because it have the noun then the article (i may have those two backwords) and finally the adjectives go afterwords in spanish. A direct translation would be ... Roberto is a boy [that is] very reserved. The words in the brackets are implied and never actually said.