Final answer:
Option a) Initiate CPR immediately is the correct answer .
Step-by-step explanation:
In the case of a cardiac arrest in a newborn where gestational age cannot be confirmed, the immediate response would be to initiate CPR. CPR stands for cardiopulmonary resuscitation, and it involves providing chest compressions and rescue breaths to help maintain blood circulation and oxygenation in the newborn's body. This is a crucial step in the resuscitation process and should be started as soon as possible(option a).