In this research at Columbia University, Charles Townes worked with ______. A: stimulated emission B: microwaves C: maser D: stimulated emission and microwaves

In his research at Columbia University Charles Townes worked with all of the following EXCEPT______. A: stimulated B: amplification C: microwaves D: a maser

In his research at Columbia University, Charles Townes worked with all of the following EXCEPT _________. A: stimulated emission B: microwaves C: light amplification D: a maser