Depending on the data all answers can be used to make it easier to read. Without more info I would go with Borders (D) since they are the best way to group the data when printed, especially if the print is in color.
Alignment would be the correct answer only if the data goes out of cell boundaries. Font Color usually makes it harder to read because of bad contrast and finally changing the Font Style has a minimal effect since the default one is already pretty readable.
