Here is a hint to this question
son means are
es means is
esta means he/she is
and estan means they are
Los maestros ____ inteligentes
Teachers ______ smart
lets take this in english terms would which one would make sense
Teachers are smart
Teachers is smart
Teachers he is smart (just took one pronoun)
Teachers they are smart
The one that says teachers are smart makes the most sense there you have your answer :son
btw i did not use google translate 4 this i actually learn spanish in school
-hope this helps