Answer
Choice B.
Work Step by Step
The original area is divided into two equal areas.
The area A of a circle of diameter d is $\frac{\pi d^2}{4}$.
We are told that $\frac{\pi d_a^2}{4}= \frac{\pi d^2}{4}$+$\frac{\pi d^2}{4}$
$\pi d_a^2=2\pi d^2$
$d = \frac{d_a}{\sqrt2}$
