Explanation:

- Section 18 of the Indian Evidence Act deals with admissions by persons from whom parties to the suit have derived their interest. This section is crucial when understanding how admissions by certain parties can be influential in legal proceedings.

- Section 12 covers the relevancy of certain facts regarding matters deemed important for legal proceedings. It focuses on proving certain facts under specific conditions.

- Section 16 involves the relevancy of the existence of any course of business. It focuses on proving the ordinary course of business under specific conditions.

- Section 13 deals with facts relevant when the right or custom is in question, focusing on the existence of any right or custom.

Correct Answer: Option 4, Section 18