If a square of area $$\frac{\text{A}}{2}$$ is cut off from a given square of area A, then the ratio of diagonal of the cut off square to that of the given square is :

• A. : 5
• B. : $$2\sqrt 5 $$
• C. : $$\sqrt 5 $$
• D. : $$\sqrt 2 $$