Only those who are gullible take every advertisement seriously.

Answer: Option C

fallible : capable of making mistakes or being wrong.
enthusiastic : having or showing intense and eager enjoyment, interest, or approval.
unsuspecting : (of a person or animal) not aware of the presence of danger; feeling no suspicion.
unrealistic : not realistic.
gullible : easily persuaded to believe something; credulous.


Synonym of gullible is unsuspecting