A light spring balance hangs from the hook of the other light balance and a block of mass M kg hangs from the former one. Then the true statement about the scale reading is

• A

  both the scales read M/2 kg each

• B

  both the scales read M kg each

• C

   the scale of the lower one reads M kg and of the upper one zero

• D

   the reading of the two scales can be anything but the sum of the reading will be M kg.