It Has Been Determined That Simon Has Gastroenteritis and the Appropriate

It has been determined that Simon has gastroenteritis and the appropriate health care provider orders Tylenol for him for abdominal pain.What is the best indicator that the Tylenol is effective for Simon's pain?

A) It is verified on the numeric rating scale.
B) Simon is no longer crying.
C) Simon is sleeping in a fetal position.
D) Simon is playing happily in the crib.