The answer to your question is "yo soy argentino". It could be the last one too but it doesn't say where is he from so i would say its "yo soy argentino". <span />
The excercise states: <em>Hello, how are you? Where are you from</em>. And the reply to that is <em>Hello, my name is Roberto. </em><u>I am argentinian.</u> Because his name is Roberto and it's in singular the answer is in singular and argentino states that he is male.
