Answer:
[tex]\large\boxed{A.\ \dfrac{r+5}{(r+7)(r+7)(r-3)}}[/tex]
Step-by-step explanation:
[tex]\dfrac{r+5}{r^2+5r-14}\div\dfrac{r^2+4r-21}{r-2}=\dfrac{r+5}{r^2+7r-2r-14}\cdot\dfrac{r-2}{r^2+4r-21}\\\\=\dfrac{r+5}{r(r+7)-2(r+7)}\cdot\dfrac{r-2}{r^2+7r-3r-21}\\\\=\dfrac{r+5}{(r+7)(r-2)}\cdot\dfrac{r-2}{r(r+7)-3(r+7)}=\dfrac{r+5}{(r+7)(r-2)}\cdot\dfrac{r-2}{(r+7)(r-3)}\\\\\text{canceled}\ (r-2)\\\\=\dfrac{r+5}{(r+7)}\cdot\dfrac{1}{(r+7)(r-3)}=\dfrac{r+5}{(r+7)(r+7)(r-3)}[/tex]
