[单选题]
Light of wavelength ,5k1 2hwo uzlu,ope/o5 9c-r x,l(auai75 nm falls on a double-slit and the third order bright fringe is seenar a9x(u,c il- 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. $20 \; mm$
