Which batch control total generally has no other purpose than control?

$($a$)$ Control totals.

$($b$)$ Hash totals.

$($c$)$ Item counts.

$($d$)$ Record counts.

The process of encoding data so that it may only be read by someone havin a key is called:

$($a$)$ A coding scheme.

$($b$)$ Check digit.

$($c$)$ Encryption.

$($d$)$ Dependency check.