If `D ,Ga n dR` denote respectively the number of degrees, grades and radians in an angle, then `D/(100)=G/(90)=(2R)/pi` (b) `D/(90)=G/(100)=R/pi` (c) `D/(90)=G/(100)=(2R)/pi` (d) `D/(90)=G/(100)=R/(2pi)`