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^(@)`, the twist angle at the joint will be
A. `theta//4`
B. `theta//2`
C. `5 theta//6`
D. `8 theta//9`