Which of the following errors would probably be corrected by key verification of data input?

(a) A salesperson manually enters an incorrect product number on a sales invoice, which is subsequently given to a data entry operator in the information systems department for key transcription to machine-readable format.

(b) A data entry operator in the information systems department mistypes a product number on a sales invoice when keying the document to machine-readable format.

(c) Both a and b

(d) Neither a nor b