A cycle tube has volume 2000 cm³. Initially the tube is filled to (3/4)^th of its volume by air at pressure of 10⁵ N/m². It is to be inflated to a  pressure of 6 × 10⁵ N/m² under isothermal conditions. The number of strokes of pump, which  gives 500 cm³ air in each stroke, to inflate the tube is

• A

  21

• B

  12

• C

  42

• D

  11