Step 1: Know the function of each hormone
Vasopressin (also called antidiuretic hormone) helps the body retain water and constrict blood vessels, thus increasing blood pressure.
Testosterone and Estrogen are sex hormones.
Oxytocin is involved in childbirth and bonding.
Step 2: Analyze the target of the question
Blood pressure regulation depends on fluid retention and vessel constriction, both managed by vasopressin.
Hence, Vasopressin is the correct hormone.