The correct answer is B. Binary digits.
Binary digits, or bits, are the basic units of information in computing and digital communications. A bit can be either a 0 or a 1, representing the electrical values of off or on, respectively. Bits are used to represent numbers, letters, and other symbols.
Octal digits are a base-8 number system that uses the digits 0-7. Octal digits are often used in computing to represent binary numbers in a more compact form. For example, the binary number 10101010 can be represented in octal as 1234.
Hexadecimal digits are a base-16 number system that uses the digits 0-9 and the letters A-F. Hexadecimal digits are often used in computing to represent binary numbers in a more compact form. For example, the binary number 10101010 can be represented in hexadecimal as 6A.
Decimal digits are a base-10 number system that uses the digits 0-9. Decimal digits are the most common number system used in everyday life.
Therefore, the correct answer is B. Binary digits.