Which graph represents the function on the interval [−3, 3] ?

Are the brackets around the x a floor or ceiling function? I can't tell, so I am unable to tell what it is.

y = floor ( x)  - 3

Let's plot a few values

x = 1  ....floor  = 1  so     y = -2

x = 1.5 ....floor = 1   so    y =  -2 

x = 2   ....floor = 2  so         y = -1

So....the points   (1, - 2)   (1.5, -2)   and ( 2, - 1)    are on the graph

Notice that these points only exist on graph  "D"