If the area of a circle is A, radius of the circle is r and circumference of it is C, then which one of the true?

Answer: Option A

Area of circle = A
Radius of circle = r
Circumference of circle = C
πr² = A . . . . . . (i)
2πr = C . . . . . . (ii)
From equation (i) ÷ equation (ii)
$$\begin{array}{rl}& \frac{\pi {\text{r}}^2}{2\pi \text{r}}=\frac{\text{A}}{\text{C}}\\ & \frac{\text{r}}{2}=\frac{\text{A}}{\text{C}}\end{array}$$
rC = 2A