Which statement about check digits is true?

• A. They are used to check the presence of data.
• B. They ensure data uses the correct currency symbol.
• C. They confirm the length of the input.
• D. They help detect errors in a sequence by providing an extra check digit.

Answer: (D)

Check digits are extra digits appended to a data sequence and computed from the other digits to reveal mistakes that can happen when data are entered or transmitted. Because the check digit is derived from the rest of the data, the system can recalculate it and compare; if it doesn’t match, an error is detected. This is why the statement about check digits is true: they help detect errors in a sequence by providing an extra check digit. They are not meant to verify the presence of data, ensure currency symbols, or confirm the input length. They focus on integrity, catching mistakes such as a single incorrect digit or a transposition in many commonly used schemes, like ISBNs or credit card numbers.