What Is the Main Feature of 'Sparse Data

What is the main feature of 'sparse data'?

A) The end report shows all possible data values within a grouping, irrespective of whether they exist.
B) This is data generated from web services and sensor or environmental systems, but not every option on a page is accessed and only data that is accessed is recorded.
C) An empty value is used where no data exist. The cube stores the real data values and the empty values are easily addressable and query-able.
D) None of the above.