. A concave mirror is placed at the bottom of an empty tank with face upwards and axis vertical.
When sunlight falls normally on the mirror, it is focussed at distance of 32 cm from the mirror. If the tank filled with water upto a height of 20 cm, then the sunlight will now get focussed at
A. 16 cm above water level
B. 9 cm above water level
C. 24 cm below water level
D. 9 cm below water level