Which of the Following Is True About Indexes, in General

Multiple Choice

Which of the following is true about indexes, in general?

A) An index can only be built over a field that has unique values.
B) Only one field of a file can be indexed.
C) An index can be used to retrieve the records of a file in logical sequence based on the indexed field.
D) An index cannot be built over a combination of fields of a file.
E) The updating of an indexed field in a record requires that the index be updated but record insertions and record deletions do not require any index to be updated.