若圆 (x−a)2+(y−a)2=4 上总存在两点到原点的距离为1，则实数 a 的取值范围是（    ）

A：$\left(-\frac{\sqrt{2}}{2},0\right)\cup \left(0,\frac{\sqrt{2}}{2}\right)$

B：$\left(-2\sqrt{2},-\sqrt{2}\right)\cup \left(\sqrt{2},2\sqrt{2}\right)$

C：$\left(-\frac{3\sqrt{2}}{2},-\frac{\sqrt{2}}{2}\right)\cup \left(\frac{\sqrt{2}}{2},\frac{3\sqrt{2}}{2}\right)$

D：$\left(-\infty ,-\frac{3\sqrt{2}}{2}\right)\cup \left(\sqrt{2},+\infty \right)$