A room (cubical) is made of mirros. An insect is moving along the diagonal on the floor such that the velocity of image of insect on two adjacent wall mirrors is `10(cm)/(sec)`. The velocity of image of insect in ceiling mirror is
A. `10 cms^(-1)`
B. `20 cms^(-1)`
C. `(10)/(sqrt2) cms^(-1)`
D. `10 sqrt2 cms^(-1)`