Question

an aed restores the hearts normal rhythm by delivering
antibiotics into the system.
a salt solution into the system.
an electric shock into the system.
vitamins into the system.

Explanation:

An AED (Automated External Defibrillator) works by delivering an electric shock. Antibiotics fight infections, a salt solution is for hydration or other medical needs not related to heart rhythm restoration in this context, and vitamins are for general health support. None of these (antibiotics, salt solution, vitamins) are used by an AED to restore heart rhythm. The key function of an AED is the electric - shock delivery to correct abnormal heart rhythms.

Answer:

an electric shock into the system.