Someone answer and explain ! they are asking which is the graph of function f, and if it’s not one of the graphs that are showing also state in you comment that it must be the fourth graph that isn’t showed in the picture you so !

Check the picture below.

the piecewise function, has two subfunctions or behaviours, one if x < 1, meaning less, not equals, but less than 1, so it doesn't include one, so it has a "hole" on that endpoint.

and the second behaviour of the piecewise is if x ⩾ 1, larger or equals than 1, so it includes 1, so it has a solid ball on that endpoint.