A body cools according to Newton's law of cooling from $100^\circ C$ to $60^\circ C$ in $20$ minutes. The temperature of the surroundings being $20^\circ C$, then the total time required for the body to cool down to $30^\circ C$ is

  • A
    90 minutes
  • B
    1 hour and 10 minutes
  • C
    80 minutes
  • D
    60 minutes

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