In the YDSE 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

   

	Column I		Column II
a)	$\Delta x$ at P will	p)	Increase
b)	Fringe width will	q)	Decrease
c)	Fringe Pattern	r)	Remain same
d)	Number of fringes between O and P will	s)	Shift downwards