A rod of length l and radius r is jointed to a rod of length l/2 and radius r/2 of same material . The free end of small rod is fixed to a rigid base and the free end of larger rod is given twist of 0^{°} the twist angle at a joint will be

A)Ø/4

B)Ø/2

C)5Ø/6

D)8Ø/9