下列运算中，错误的是 (   )

A：$3\sqrt{2}-2\sqrt{2}=\sqrt{2}$

B：$\frac{1}{\sqrt{2}}=\frac{\sqrt{2}}{2}$

C：$\sqrt{2}+\sqrt{3}=\sqrt{5}$

D：$\sqrt{2}.\sqrt{3}=\sqrt{6}$