The incorrect syntax for axvline() function is C. plt.axvline(y, xmin, xmax, linewidth. This is because axvline() is used to draw a vertical line on a plot at a specific x-coordinate, so y parameter is not applicable. Additionally, the correct syntax for axvline() function should include the x-coordinate parameter followed by any optional parameters such as ymin, ymax, and label. The correct syntax examples are:
A. plt.axvline(x='text')
B. plt.axvline(x, ymin=0, ymax=1, label='text')