Choice "D" is correct. If a random number matches a properly voided voucher, the auditor would ordinarily replace this with another voucher in order to attain the desired sample size.
Choice "a" is incorrect. A voucher that cannot be located is normally considered a deviation.
Choice "c" is incorrect. The auditor would be particularly concerned with a voided voucher that represents a material amount, but this fact alone would not cause selection of another voucher. Determination of whether to select another voucher or to instead consider this a deviation would depend on whether the voucher was properly voided.
Choice "b" is incorrect. If the voided voucher indicates a control deviation, then it would be counted as such.