New bathroom in basement...vent question

I am just about to start to finish my basement. We bought the house nine months ago and had a "two piece rough in" put in. There are 2 pipes coming out of the floor. One is about 4 inches (I am guessing for the toilet) and another pipe that is about 2 inches. I am not sure what they are for and if this has to be vented. There is only one other pipe in the floor (not very close and I believe it is a clean out.) Any help/ideas would be great. Thank you.




MF

Maybe one pipe for toilet, and one for lavatory sink. Most definitly needs to be vented. Perhaps a vent is tied in where these pipes join the main?

Pictures might help...
Give us an idea of layout...
As well, in the pictures, place a tape for size comparison....

How big's the cleanout? Is it coming from the floor? If it's 2", then perhaps it's a vent for the two fixtures. For the other 2" stub, if you can If you can see water in it, (you'll have to fill it first) then it might be a shower / tub drain.