<span>Él es un compañero de clase is the right answer. The 1st sentence is ella but </span>compañero should be compañera. In the second one ella should not have an accent mark and in the last one el doesn't match with una.
Answer:
Intonation:
¿Manos a la obra?
Tag Questions:
Manos a la obra, ¿no?
Explanation:
First one is an intonation as there is a pitch in the statement
Second is a tag question therefore using ¿no? at the end
The word is prohibe, for example se prohibe ir al armario durante la clase
