Engine & Internal - just got a b16

hey i just got my b16 and i heard people say that they have 2 O2 sensors. is that for all of them cause i just got 1 of them and its at the bottom.

i have a jdm b16a(2) and it only has 1, but my old 00 si had 2. I think the obd1 has 1, and obd2 has 2.

so what is that wire hanging close to the radiator it has a green connector? if it helps its also a jdm 91.