What fills in all three of these blue boxes?
ABC-DEF-GHI-JKL-MNOP-QRSTUV-WXYZ - All of the other answers have three alphabetically-consecutive letters. The "mystery" question in the Description above is an innocuous-looking pangram (meaning that it contains all 26 letters at least once). "I'll spell it out for you" is the primary clue up there. And yes, I considered both "Xamine Your Zipper" and "hydroxyzine" questions for XYZ.