An index is clustered, if
Answer is C).
Index can be created using any column or combination of column which need not be unique. So, A, B are not the answers.
Indexed column is used to sort rows of table.Whole data record of file is sorted using index so, C is correct option. (Simple video explains this).
Clustered Index is created on data file whose file recordrds are physically ordered on a non key field which does not have distinct value for each record .
Option A ) Candidate Key
Option B) Primary Key
Option D ) File NOT ordered
Best choice is Option C
Option C ) Data records are ordered