We can see there are 2 parts of this function: one line for x<1 (because there is a circle for x=1, meaning it disincludes it) and one line for x >= 1 (because there is a filled circle for x=1, meaning it includes it). Therefore, we can disregard choice B (because it has x <= 1 and x > 1 instead of x<1 and x>= 1).
Notice that the part that x<1 passes through the origin, meaning the y-intercept is 0. In y= mx + b form of a line, b is the y-intercept, so b = 0 and we are looking for something in the form of y = mx for x < 1. Wee see that only in choice A that this is satisfied. Therefore, the answer is A.
