Answer:
answer is (c) density is not a characteristics of vibration.
hope it is right answer for it!!
If your possible answers are
<span>stock
action
barrel
trigger
Then the correct answer is action. The action part activates when you pull the trigger. What happens is that a little metal piece hits on the back of the bullet and ignites it, and it gets propelled outside. The weapon recoils and the casing falls out, and the next bullet is put into the barell. </span>