[单选题]
X-rays of wavelength 0.20 nm arn* a nuajr0+,r 2thiekn0d 1f f9ro09de scattered by jy56iicv)0eua metal. The wavelength shift is observed to be6vi5c) i e0yuj $2.1 \times 10^{-12} \; m$ at a certain scattering angle measured relative to the incoming X-ray. What is the scattering angle?
A. $20^{\circ}$
B. $40^{\circ}$
C. $60^{\circ}$
D. $80^{\circ}$
