The answer is Its.
Theirs/their pertains to more than one person belonging to items.
It's is a contraction form of "it is".
The first sentence is the correct sentence
The correct answer is the last one. Kilpatrick's article shares how White House staff feels about Nixon's resignation.
In the article, numerous aides and officials are quoted. Each gives his thoughts and/or opinions on Nixon's resignation. Many are sorry to see him go. Therefore the second option -- that the staff is unaffected -- is not correct.
The article does not say much about who will become president after Nixon. Furthermore, the staff itself is not changing; only Nixon is leaving. Therefore, the final answer is the correct one.
This is the Newton’s third law of motion buddy: If an object A exerts a force on object B, then object B must exert a force of equal magnitude and opposite direction back on object A. Hope it helps :D
