The following figure shows two air-filled bulbs connected by a U-tube partly filled with alcohol What happened to the levels of alcohol in the limbs X and Y when an electric bulb placed midway between the bulbs is lighted?

• A

  The level of alcohol in limb X falls while that in limb Y rises

• B

  The level of alcohol in limb X rises while that in limb Y falls

• C

  The level of alcohol falls in both limbs

• D

  The level of alcohol rises in both limbs