Which of the following statement(s) is/are true regarding standard costs and cost variances?

i. they can be used in performance evaluation of managers and divisions.

ii. management by exception is used by managers in deciding whether to investigate cost variances.

iii. variance investigation involves looking at only unfavourable variances.

iv. a shorter product life cycle means that standard cost data are only relevant for a shorter time period.

v. using unskilled workers may result in a favourable labour efficiency variance.