Which pipes are what in this basement rough-in?
The small one in the top left coming out of the floor is likely for a shower or tub. The larger diameter pipe coming out of the floor is almost certainly for a toilet. The smaller pipe to the right of the toilet that continues up is for the lavatory (i.e. sink). 

You can tell these things because:


The toilet requires a 3" rough-in.
Showers and tubs require rough-ins within the floor and the rough-in must contain a P-trap. So you can confirm that pipe in the top left is for a shower or tub by taking off the cap and pouring some water in it. If it "fills up" some before draining, you'll know it has a P-trap and is indeed for a shower or tub.
The sanitary tee in the pipe that continues up is placed approximately correctly for a vanity sink.