Oxygen (O2) Sensor

I have a 1997 Maxima SE. Can someone please tell me if the rear o2 sensor is the one near the manifold or near is it pipe mounted.

The reason I asked is becuase my check engine light is on, I ttok it to Nissan, and they told me I need a REAR O2 SENSOR. So I want to do it myself and I want to make sure I buy the correct one.

Thanks

the rear O2 sensor is the one furthest from the front of the vehicle, the one near the manifold is the front O2 sensor.