In the YSDE apparatus shown in figure, ${\Delta }_X$ is the path difference between $S_{2}P$   and  $S_{1}P$.  Now a glass slab is introduced in front of $S_2$  , then match the following.

A)	${\Delta }_X$  at P will	p)	increase
B)	Fringe width will	q)	decrease
C)	Fringe pattern will	r)	remain same
D)	Number of fringes between O and P will	s)	Shift downwards