When an object is kept at a distance of 30 cm from a concave mirror, the image is formed at a distance of 10 cm. If the object is moved with a speed of 9 cms⁻¹ in horizontal direction, the speed with which the image moves is

A. 0.1 cm/s
B. 1 cm/s
C. 3 cm/s
D. 9 cm/s