The correct answer is C. Binary.
Binary is a base-2 numeral system, often used by computers and other electronic devices to represent numbers. It is a system that uses two digits, 0 and 1, to represent numbers. Each digit is called a bit, and a group of bits is called a byte.
Decimal is a base-10 numeral system, the most common system of numeration in use today. It is a system that uses ten digits, 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9, to represent numbers.
Octal is a base-8 numeral system, used primarily as a human-readable representation of binary data. It is a system that uses eight digits, 0, 1, 2, 3, 4, 5, 6, and 7, to represent numbers.
None of the above is not a valid answer.