Instruction : Answer the questions given below on the basis following figure.

A and B are centres of the circles whose radii are respectively `r_1 and r_2` PNM is a direct common tangent touching the circles respectively at M and N.
Length of MN is

Options

A. A)`sqrt( d^(2) - ( r_1 -r_2)^2) `
B. B)`sqrt( d^(2) + (r_1 - r_2)^2)`
C. C)`d^(2) - ( r_1 - r_2)^2`
D. D)`d+ sqrt( (r_1 - r_2)^2)`

Answer

A