Concept: CCC stands for Classified Catalogue Code, developed by Dr. S. R. Ranganathan. It gives rules for preparing catalogue entries in a systematic manner.
Step 1: Understand the sections of main entry in CCC.
A main entry in CCC contains important sections such as leading section, title section, note section, accession number and tracing section.
\[
\text{CCC Main Entry} \Rightarrow \text{Leading Section + Title Section + Tracing}
\]
Step 2: Check the given items.
Leading Section is a part of the main entry.
Title is also a part of the main entry because it identifies the document.
Tracing is also included because it shows additional entries made in the catalogue.
\[
A = \text{Leading Section}
\]
\[
C = \text{Title}
\]
\[
E = \text{Tracing}
\]
Step 3: Reject unsuitable items.
ISBN is mainly related to book identification in modern bibliographic description. Publisher is part of imprint information, but in the given CCC section list, it is not selected as an independent section.
Therefore, the correct set is:
\[
A,\ C,\ E
\]