here is the simple no-theory answer:

a C2 has the 2 note of the C scale.
the 2 note of the C scale is D.
so, a C2 has a D.

I like to play it like this:


E |-------------------------------|
B |-----------3-(d)---------------|
G |-----------0-(g)---------------|
D |-----------2-(e)---------------|
A |-----------3-(c)---------------|
E |-------------------------------|