The correct answer is: C. Misaligned print head
A dot matrix printer prints text and images by striking an inked ribbon against paper with a series of pins. The pins are arranged in a matrix, and the number of pins determines the resolution of the print.
If the print head is misaligned, the pins will not strike the paper evenly, resulting in light and dark areas on the printout.
Erratic paper advancement can also cause light and dark areas on the printout, but this is usually due to a problem with the paper feed mechanism, not the print head.
Erratic ribbon advancement is less likely to cause light and dark areas on the printout, but it can happen if the ribbon is not properly installed or if it is old and worn.
Overheating print head is also less likely to cause light and dark areas on the printout, but it can happen if the printer is used for long periods of time without being allowed to cool down.
In conclusion, the most common cause of light and dark print on a dot matrix printer is a misaligned print head.