Answer:
4. Their
Explanation:
Things to help you understand better:
Their is the possessive pronoun, as in "their car is red"; there is used as an adjective, "he is always there for me," a noun, "get away from there," and, chiefly, an adverb, "stop right there"; they're is a contraction of "they are," as in "they're getting married."
This is present simple form.
Hades does not believe that the other gods will help him search for the Helm of Darkness, so he doesn't tell any of the other guards that it is missing. Eventually, Percy helps him find the Helm of Darkness that was stolen by Luke, so Hades helps Percy out and returns his mother.