Answer:
The formula gives the circumference of a circle:
C = πd
Where d is the diameter of the circle.
Substituting the given values, we get:
C = (22/7) x 21 cm
C = 66 cm (approx)
Therefore, the circle's circumference with a diameter of 21 cm, approximated using π equals 22/7, is 66 cm.
So, the correct option is (C) 66 cm.