Which is the graph of the step function f(x)?

f(x) = StartLayout Enlarged left-brace 1st row 1st column negative 1 2nd column x less-than negative 1 2nd row 1st column 0 2nd column negative 1 less-than-or-equal-to x less-than-or-equal-to 1 3rd row 1st column 1 2nd column x greater-than 1 EndLayout

On a coordinate plane, a piecewise function has 3 lines. The first line has an open circle at (negative 3, negative 1) and continues horizontally to an open circle at (negative 1, negative 1). The second line has a closed circle at (negative 1, 0) and continues horizontally to a closed circle at (1, 0). The third line has an open circle at (1, 1) and continues horizontally to an open circle at (3, 1).
On a coordinate plane, a piecewise function has 3 lines. The first line has an open circle at (negative 1, negative 1) and continues horizontally to the left at y = negative 1. The second line has a closed circle at (negative 1, 0) and continues horizontally to a closed circle at (1, 0). The third line has an open circle at (1, 1) and continues horizontally to the right at y = 1.
On a coordinate plane, a piecewise function has 3 lines. The first line has a closed circle at (negative 1, negative 1) and continues horizontally to the left at y = negative 1. The second line has an open circle at (negative 1, 0) and continues horizontally to an open circle at (1, 0). The third line has a closed circle at (1, 1) and continues horizontally to the right at y = 1.
On a coordinate plane, a piecewise function has 3 lines. The first line has an open circle at (negative 3, negative 1) and continues horizontally to an open circle at (negative 1, negative 1). The second line has an open circle at (negative 1, 0) and continues horizontally to an open circle at (1, 0). The third line has an open circle at (1, 1) and continues horizontally to an open circle at (3, 1).