Which of the following statements about direct or indirect classifications is right?

Question $9$Select one:

a$.$

The physical documents in paper can only be classified by direct classification method.

b$.$

Indirect classification is useful only if we classify electronic records.

c$.$

Direct classification is classifying files by locating them in physical locations, but indirect classification uses the index to classify the files.

d$.$

Direct classification is useful only if we classify paper$-$based records.