Music notation help please

[traviata]

I thought this might be a good place to ask...

DD has music homework. She has been given the note letter names, and has to write them on the stave, eg A, C, G E etc. No problem with this.

However, some of the note letter names have a small mark by them, like an apostrophe. What does this mean?
E'
B'
and so on.

I have never come across this, and I can't find anything online.

Below ledger lines - 8va bassa

piano.about.com/od/musicaltermsa1/g/GL_8vb.htm

Yes - use of C, C', C' ' perfectly common.