Answer:
After “grade”
Kari and Misha, who have known each other since first grade, are both yearbook editors and photographers.
Explanation:
This sentence's main point is: Kari and Misha are both yearbook editors and photographers.
However, while giving the main point, we can give the reader a little more information by telling them: "who have known each other since first grade" [identity of Kari and Misha]
E.g. Roller coaster and bumper cars, which are often found in theme parks, are really fun to ride.
This sentence's main point is: Roller coaster and bumper cars are really fun to ride.
However, while giving the main point, we can give the reader a little more information by telling them: "which are often found in theme parks" [where roller coasters and bumper cars are found]
