[单选题]
Light of wavelength 575 nm falls on a double-slit and the thbufpi/a 9jd +1ird order bright -n)q+kw8d z:ploqo y:fringe ipq) -yqozolndw8+ k:: s seen at an angle of $6.5^{\circ}$. What is the separation between the double slits?
A. $5.0 \; mm$
B. $10 \; mm$
C. $15 \; mm$
D. $20 \; mm$
