(solution) The Franck-Hertz experiment demonstrated which of the following?

(solution) The Franck-Hertz experiment demonstrated which of the following?

The Franck-Hertz experiment demonstrated which of the following? 

Atoms colliding with electrons absorb energy in discrete amounts.

Atomic spectra are characteristic of the elements.

The absorption of light causes a change in energy ?E = h?

A and C

All of the above

I was thinking (A and C) but can someone verify