The correct answer for why internet communication uses optical fiber cables is option 3 - high data carrying capacity.

Option 1 - low cost: This option is not the main reason for using optical fiber cables for internet communication. While cost is a factor, it is not the primary reason.

Option 2 - free from virus threat: This option is not the main reason either. Optical fiber cables are not inherently immune to virus threats. The security of internet communication is typically addressed through other means, such as encryption and firewalls.

Option 3 - high data carrying capacity: This is the main reason for using optical fiber cables. Optical fiber cables have a much higher capacity for carrying data compared to other transmission mediums like copper cables. They can transmit large amounts of data quickly and efficiently.

Option 4 - faster than light communication of signals: This option is incorrect. While optical fiber cables can transmit data at very high speeds, they cannot exceed the speed of light. The speed at which signals travel through the cables is close to the speed of light, but not faster.

In conclusion, the main reason for using optical fiber cables in internet communication is their high data carrying capacity.