Question: You've just plotted some data and want to change the color behind the lines you've plotted to black. Which code block will accomplish this?

1. `h_f = figure; set(h_f,'Color', [0 0 0]);`
2. `h_a = gca; set(h_a,'Color', [0 0 0]);`
3. `h_a = axes; set(h_a,'Color', [0 0 0]);`
4. `h_f = gcf; set(h_a,'Color', [0 0 0]);`

Answer: The correct answer of the above question is Option B:`h_a = gca; set(h_a,'Color', [0 0 0]);`