#### Answer

Choice D.

#### Work Step by Step

Equation 24-3b, $sin \theta = \frac{m \lambda}{d}$, predicts the location of the minima for nonzero integer values of m.
If we double the wavelength in a single-slit diffraction experiment but for a given m want to keep the angle $\theta$ the same (the angle at which that minimum is seen), doubling the spacing d will accomplish that.