If a number of sine waves with modulation indices `n_(1),n_(2),n_(3)`… modulate a carrier wave, then total modulation index (n) of the wave is
A. `n_(1)+n_(2)…. +2(n_(1)+n_(2)…..)`
B. `sqrt(n_(1)-n_(2)+n_(3)…..)`
C. `sqrt(n_(1)^(2)+n_(2)^(2)+n_(3)^(2)….)`
D. none of these