A Centigrade and a Fahrenheit thermometer are dipped in boiling water. The water temperature is lowered until the Fahrenheit thermometer registers 140°. What is the fall in temperature as registered by the Centigrade thermometer ? 

• A

  ${30}^{\mathrm{o}}$

• B

  ${40}^{\mathrm{o}}$

• C

  ${60}^{\mathrm{o}}$

• D

  ${80}^{\mathrm{o}}$