D) Guard against a short circuit electrocuting a user.
"The 4-wire setup is inherently safer and better able to prevent electrical shock, which in the case of a 220/240-volt circuit can be fatal."
A believe that’s called a reference point.
Answer:
q=1.4*10^{-9}C
Explanation:
Given data:
charge on ruler = -14μC
Mass of tissue is 5 g
To Know the minimum charge, equate electrostatic force to weight
we have F = W
so
putting all value in equation,

solving for q

or q=1.4*10^{-9}C
Pressure and heat. I hope this helps