Two pistons can move freely inside a horizontal cylinder  having two sections of unequal cross-sections. The
pistons are joined by an inextensible, light string and some gas is enclosed between the pistons. On heating the system, the piston will 

• A

  move to the left

• B

  move to the right

• C

  remain stationary

• D

  (a) or (c) depending upon the initial pressure of the gas