Well, I'm not sure about two, but one Koi symbolizes "a long and healthy life".
They symbolize peace
Valleys and rivers will make a v-shape. (with the tip of the v pointing upstream)
four two upstream and two down
Assuming we are talking O2 sensors, the downstream O2 sensors left and right are the same. The upstream O2 sensor left side is left side upstream only. Upstream right side fits both left and right sides upstream only. The difference is the length of the wires for the upstream sensors.
Some think it means ''Peace Makers''. Others think that it means they are two crescent moons joined together by Earth experience and bring deep subconscious sensitivity to Earth.
Only two, upstream and downstream.
hair, the kind of swimming apparel.
There are 4. Two upstream (bank1) two downstream (bank2).
you can wear two but you might get a head ache.
Yes, the correct spelling of "swimming" does have two Ms just as it is spelled in the question.
Bi means two (for the two wheels).
Four, two before the cats (upstream) and two after the cats (downstream).