Identify the statement that best defines time$-$variant data.

a$.$ Time$-$variant data refers to data that does not change over time.

b$.$ Time$-$variant data refers to data that changes over time, with no history of data change tracking.

c$.$ Time$-$variant data refers to data that changes over time; its history of data changes must be maintained.

d$.$ Time$-$variant data refers to data that was created redundantly.