The smallest division on the main scale of a vernier callipers is `1mm`, and 10 vernier divisions coincide with 9 mainn scalel divisions. While measuring the diameter of a spehre the zero mark of the vernier scale lies between 2.0 and 2.1 cm and the fifth division of hte vernier main scale coincide with a main scale division. Then diameter of the sphere is
A. `20.5 mm`
B. `21.5mm`
C. `21.50mm`
D. `20.50mm`
