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

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 halved

A) if the distance between the slits is changed to $d ^ { \prime } = \frac { d } { 2 }$ .
B) if the wavelength is changed to $\lambda ^ { \prime } = 2 \lambda$ .
C) if the distance between the slits is $d ^ { \prime } = 2 d$ the wavelength is changed to $\lambda ^ { \prime } = 4 \lambda$ .
D) if any of the above occurs.
E) only if the width of the slits is changed to $w ^ { \prime } = 2 w$ .