If xD $=$ overhead product molal composition and RD $=$ reflux ratio, then slope and intercept of the operating line for rectifying section are respectively

$[$xD$/($RD $+1)],[$RD$/($RD $+1)]$

$[$RD$/($RD $+1)],[$xD$/($xD $+1)]$

$[$xD$/($RD $+1)],[($RD $+1)/$RD$]$

None of these