A
A.$frac{{partial {{boldsymbol{dot r}}_i}}}{{partial {{dot q}_k}}} = frac{{{rm{d}}{boldsymbol{r}_i}}}{{{rm{d}}{q_k}}}$
B
B.$frac{{partial {{boldsymbol{dot r}}_i}}}{{partial {q_k}}} = frac{{partial {boldsymbol{r}_i}}}{{partial {{dot q}_k}}}$
C
C.$frac{{partial {{boldsymbol{dot r}}_i}}}{{partial {{dot q}_k}}} = frac{{partial {boldsymbol{r}_i}}}{{partial {q_k}}}$