Bright and Dark Fringes Are Seen on a Screen When $\lambda ^ { \prime } = \frac { ? } { 2 }$

Multiple Choice

Bright and dark fringes are seen on a screen when light from a single source reaches two narrow slits a short distance apart.The number of fringes per unit length on the screen can be doubled

A) if the distance between the slits is doubled.
B) if the wavelength is changed to $\lambda ^ { \prime } = \frac { ? } { 2 }$ .
C) if the distance between the slits is quadruple the original distance and the wavelength is changed to $\lambda ^ { \prime } = 2 \lambda$ .
D) if any of the above occurs.
E) only if the width of the slits is changed to $w ^ { \prime } = \frac { w } { 2 }$ .