Which musical form is an example of renaissance choral music sung in church?
a cappella
estampie
organum
madrigal

The best and most correct answer among the choices provided by the question is organum.

 Organum, a preexistent chant is embellished by the addition of other voices singing different music. When music is made up of people singing or playing different lines at the same time, it is said to be polyphonic.        

Hope my answer would be a great help for you.    

Net  the suffix is your .com/.net/.org, and so on, i believe