What are these two drains for?
If the large pipe is 12 1/2", 13 1/2" or so (it could be up to 14 1/2")from the wall that will surely be for your toilet. The pipe on the right will be for your tub. The plastic that it protrudes through allows the bit of maneuvering room to get it to line up with the tub drain or it could be used for a shower, although it will be offset instead of the center. This pipe should be somewhere about 16 or so inches away from the wall on the right that is NOT in the picture. You will still need a drain for the sink.

There should be a 2" line like the ones inside the stud wall in your picture, just not there.
I would presume there is another pipe on the other side of the room?