I can exclude B because B shows maxima, but I do not know how to exclude A and D.
These are the equations for the diffraction grating and the double-slit experiment:
dSin(A) = nL
DL = ax
It seems that this problem is about the combination of both.
C is probably the correct answer.
https://physics18.weebly.com/uploads..._s17_qp_13.pdf
https://physics18.weebly.com/uploads..._s17_ms_13.pdf