The round bar shown has a varying diameter $(d_1=1\mathrm{.}5in.$ and $d_2=1\mathrm{.}0in.),$ and it supports an applied torque of $40$ in$.-$kips at Point B$.$ For $G=11,600$ ksi, the angle of twist at Point C is most nearly:

$0$

$4\mathrm{.}0$

$12$

$24$