Question

which of the following is part of a shotgun shell?
the trigger
the bullet
the powder
the firing pin

Explanation:

Shotgun shells contain propellant powder as a core component. The trigger and firing pin are parts of the shotgun itself, not the shell; shotgun shells use shot (a collection of small pellets) or a slug, not a single "bullet" (a term for a single projectile in a rifle/handgun cartridge).

Answer:

The powder