How many O2 sensors in a 96 conti

[lostinbass]

Can anyone tell me how many O2 sensors a 96 continental has?
Got a service engine soon light..code said it was an O2 sensor, the front("before" )one. HAd one replaced, less than 100 miles it went on again, reset it, about 100-200 miles, on again.
Could there be more than one front sensor? Should I replace the back one(s).
Could it need a tune up? Should I just live with it..the car runs great..I HATE that light!
thanks

 

[formerknown]

4- two before the cats in the manifold, two after the cats to check catalyst efficiency...

 

[lostinbass]

Thanks,
I guess the mechanic could of installed the sensor in the one that wasnt bad, or, they both are bad.
To get more specific,Would anyone know which O2 is bank one? How would I locate a bank one upstream sensor from a bank 2 upstream sensor?
Would it make sense to replace the downstreams as well?
Any help is appreciated.