Which type of index should you use?

You have a table that contains 5 million rows. The table has a clustered index. You plan to
add an additional index on a column that contains 80 percent null values. The column is
used extensively in WHERE clauses. You need to implement an index strategy for the
column. The solution must minimize the amount of storage space required for the index.
Which type of index should you use?

A.
filtered

B.
nonclustered