A convex lens is put 10 cm from a light source and it makes a sharp image on a screen, kept 10 cm from the lens. Now a glass block (refractive index 1.5) of 1.5 cm thickness is placed in contact with the light source. To get the sharp image again, the screen is shifted by a distance d . Then d is:
a. 1.1 cm away from the lens
b. 0
c. 0.55 cm towards the lens
d. 0.55 cm away from the lens