Plz
all 4 are different and one of them is the answer.

That's the ceiling function from 1 to 4.  Let's look at some points

f(1)=1

f(1.5)=2

f(2)=2

f(2.5)=3

f(3)=3

f(3.5)=4

f(4)=4

We see at the integer x values are lower than the values half way between x and x+1.  That means the little segments are closed at the right end, dark circles and open at the left end, open circles.

That narrows it down to the second and fourth graph, with the open circles on the left.  Since f(1)=1, f(2)=2 etc, that's the second graph, not the fourth.

second graph on first photo