o2 sesor in 97 G10/Express

Hi, I got a 97 G10, 4.3.....The codes are telling me my o2 sensor at "bank1 - sensor 1" is bad....my ? is whitch sensor is this? theres one on divers side, 2 before the cat on pass side & 1 after cat on pass side. any help would be greatly appreciated......T

your '97 has two upstream and two downstream. bank1 sensor one indicates it is the first sensor in line upstream.