For a sphere, ends of a diameter have position vectors $\overline{\mathrm{a}}$ and $-\overline{\mathrm{a}}$ , then vector equation of sphere is 

Statement-I : $\left|\overline{\mathrm{r}}\right|=\left|\overline{\mathrm{a}}\right|$
Statement-II : $\left(\overline{\mathrm{r}}+\overline{\mathrm{a}}\right)·\left(\overline{\mathrm{r}}-\overline{\mathrm{a}}\right)=0$
Statement-III : $\overline{\mathrm{r}}.\overline{\mathrm{a}}=0$
Which of the above statements are true