Answer: Nando es un alumno muy ambicioso.
Explanation: We must complete the sentence:
"Nando es ____________________ alumno muy ambicioso."
A rough translation of this is:
"Nando is __ very ambitious student."
Obviusly this can be completed with an "a", but in Spanish is a bit more hard.
First, Nando is a masculine name, and Nando is a singular person, so the correct pronoun would be "Un"
Nando es un alumno muy ambicioso.