o2 sensors on 1996 Chevrolet Blazer

I have a 4.3 in my chevy blazer and need to see where my o2 sensors are so i can replace the right ones. I have my admissions test that shows sensor1(2)sensor2 and sensor1(2) sensor 3 which ones is the right one that i need to change so i can just past my test.

Asked by for the 1996 Chevrolet Blazer
the drivers side is bank 1. the passenger side is bank 2. there is no bank 3.