On dropping a stone in stationary water,circular ripples are observed. The rate of flow of ripples is $6 \text{ cm/sec}$. When the radius of the circle is $10 \text{ cm}$,the rate of increase in its area is:

  • A
    $120 \text{ cm}^2/\text{sec}$
  • B
    $60 \pi \text{ cm}^2/\text{sec}$
  • C
    $10 \pi \text{ cm}^2/\text{sec}$
  • D
    $120 \pi \text{ cm}^2/\text{sec}$

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