An object is placed at `A(OA gt f)`. Here, f is the focal length of the lens. The image is formed at B. A perpendicular is erected at O and C is chosen such that `/_BCA = 90^(@)`. Let OA = a, OB = b and OC = c. Then the value of f is

A. `((a+b)^(3))/(c^(2))`

B. `((a+b)c)/((a+c))`

C. `(c^(2))/(a+b)`

D. `(a^(2))/(a+b+c)`