The question provides the following sentence and asks us to fill in the gaps: "Janelle and Marcus and _______ group went to the library to prepare for the presentation, but the specific book they needed wasn't _______.
The first gap refers to the group of Janelle and Marcus - so it's a group that belongs to them, or their group (possesive)
The second gap refers to a place where they expected the book, and the word is "there" - it's not an abbreviation so no apostrophe is needed.
Answer: their, there
