A rod of length l and radius r is joined 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 a twist of \[\theta {}^\circ \], the twist angle at the joint will be [RPET 1997]

• A.                 \[\theta /4\]             
• B.                 \[\theta /2\]
• C.                 \[5\theta /6\]          
• D.                 \[8\theta /9\]