B. El maestro is the correct answer :)
Answer:
And because wickedness has multiplied, the love of many will grow cold.
Explanation:
hola
Ayer tú (cantar) una canción.
Yesterday you (to sing) a song.
Answer: Ayer tú cantaste una canción.
Yesterday you sang a song.
Cantaste is 2nd person singular which matches tú (you).