A dot matrix printer is a type of printer that uses a matrix of small pins to create characters or images on paper. Let's analyze each statement to determine the correct answer:
i) Prints an entire line at a time: This statement is incorrect. A dot matrix printer prints one character at a time by striking an ink-soaked ribbon against the paper. It does not print an entire line at a time.
ii) Is a non-impact printer: This statement is incorrect. A dot matrix printer is an impact printer because it uses physical force to create the characters. The pins strike the ribbon, which transfers ink to the paper, resulting in the printed output.
iii) Allows multiple copies to be taken at a time: This statement is correct. Dot matrix printers have the ability to create multiple copies simultaneously. This is achieved by using carbon paper or carbonless paper, which allows the impact of the pins to transfer the image to multiple layers of paper.
iv) Prints one character at a time: This statement is correct. Dot matrix printers operate by individually striking pins against an ink-soaked ribbon to create characters. Each pin represents one dot, and the combination of dots forms the characters or images on the paper.
Based on the analysis above, the correct answer is C: iii and iv. A dot matrix printer allows multiple copies to be taken at a time and prints one character at a time.

Dot matrix printers are a type of printer that use a matrix of small pins to create dots that form characters and images on the paper. In this question, we are given four statements about dot matrix printers and we need to determine which statements are true.

i) Dot matrix printers print an entire line at a time.
ii) Dot matrix printers are non-impact printers.
iii) Dot matrix printers allow multiple copies to be taken at a time.
iv) Dot matrix printers print one character at a time.

Let's analyze each statement to determine if it is true or false:

i) Dot matrix printers print an entire line at a time.
This statement is true. Dot matrix printers have a print head that contains a matrix of pins. These pins strike an ink ribbon, transferring ink onto the paper and forming characters and images. The print head moves horizontally across the paper, printing one line at a time.

ii) Dot matrix printers are non-impact printers.
This statement is true. Non-impact printers are printers that do not physically strike the paper to create an image. Dot matrix printers use pins to strike an ink ribbon, which then transfers ink onto the paper. This method is considered non-impact as there is no direct contact between the print head and the paper.

iii) Dot matrix printers allow multiple copies to be taken at a time.
This statement is true. Dot matrix printers can create multiple copies by using carbon paper or carbonless paper. The print head strikes the ink ribbon and presses it against the carbon paper, transferring ink onto multiple sheets of paper simultaneously. This allows for the creation of multiple copies in one print job.

iv) Dot matrix printers print one character at a time.
This statement is false. Dot matrix printers print multiple dots simultaneously to form characters and images. The print head contains a matrix of pins, and each pin corresponds to a dot on the paper. By selectively striking the pins, characters and images are formed by a pattern of dots.

In conclusion, the true statements about dot matrix printers are:
- Dot matrix printers print an entire line at a time.
- Dot matrix printers are non-impact printers.
- Dot matrix printers allow multiple copies to be taken at a time.