theirs

"You must do your homework before you can watch television."

"For a change, in this case, he was telling the truth."

"My sister brought several books to the library, and that one is about dinosaurs. "

"They brought their books with them."

"Be sure to finish your homework before you go to bed!"

"Where does this document belong?"

"Follow that car!"

"Go easy on him: he is but a child."

"The possessive case of the word "student" is "student's". "

"By now, you must surely know which is which."

"The children asked their teacher for help with those math problems; she explained them. "

"The school is located just outside the town, without the main shopping area. "