To solve this question, the user needs to know the basic unit of digital storage and its prefixes.

The basic unit of digital storage is a bit, which is represented by either a 0 or a 1. A byte is a group of 8 bits. The prefixes used to represent large amounts of bytes are kilo, mega, giga, and tera.

Now, let's go through each option and explain why it is right or wrong:

A. 10^6: This option is incorrect. One megabyte (MB) is equal to 10^6 bytes. One terabyte (TB) is equal to 10^12 bytes, which is a much larger quantity than 10^6.

B. 10^9: This option is incorrect. One gigabyte (GB) is equal to 10^9 bytes. One terabyte (TB) is equal to 10^12 bytes, which is a much larger quantity than 10^9.

C. 10^12: This option is correct. One terabyte (TB) is equal to 10^12 bytes. This is a very large quantity of data, and is often used to represent the storage capacity of hard drives and other digital storage devices.

D. 10^15: This option is incorrect. One petabyte (PB) is equal to 10^15 bytes. One terabyte (TB) is a much smaller quantity of data than 10^15 bytes.

Therefore, the answer is: C. 10^12