What are the factors to be considered to adjust your speaking volume in presentation?

A、thesizeoftheroom:howlargeistheroom?;
B、thesizeoftheaudience:howmanylistenersarethere?;
C、thelevelofbackgroundnoise:isitnoisyorquiet?;
D、theavailabilityofamicrophone:canyouuseamicrophone?