Which Two of the Following Equations Do Not Correctly State $\frac{\mathrm{d}}{\mathrm{t}}=\mathrm{r}$

Multiple Choice

Which two of the following equations do not correctly state the relationship between distance, rate and time?
(a) $\frac{\mathrm{d}}{\mathrm{t}}=\mathrm{r}$
(b) $\mathrm{dr}=\mathrm{t}$
(c) $\frac{\mathrm{r}}{\mathrm{t}}=\mathrm{d}$
(d) $\frac{\mathrm{d}}{\mathrm{r}}=\mathrm{t}$

A) (a) & (c)
B) (b) & (c)
C) (a) & (d)
D) (b) & (d)