Final answer:
The equation x = -3 is a vertical line where all points have an x-coordinate of -3, making the correct answer b. x = -3.
Step-by-step explanation:
The equation of the line x = -3 is a vertical line, which means that for all points on this line, the x-coordinate is -3, and the y-coordinate can be any real number. Therefore, the correct answer is b. x = -3. Options a, c, and d represent horizontal lines or different vertical lines, which are not accurate descriptions of a vertical line crossing the x-axis at -3.