Explanation:

- Section 32: This section covers cases where statements of persons who cannot be called as witnesses are considered relevant under certain circumstances. It includes statements made during deathbed, explosive statements, or ones made under unavoidable circumstances. This is the section that incorporates the necessity rule as to admissibility of evidence.

- Section 33: This section relates to the relevance of evidence given in previous judicial proceedings if the witness is now unavailable. It’s relevant in terms of ensuring continuity and consistency in evidence presentation.

- Section 31: It describes the admission of facts, where the relevance of evidence is concerned with admissions made by parties in the suit. However, it does not directly relate to necessity rules.

- Section 45: This deals with opinions of experts in the context of evidence, allowing expert opinions to be admissible in court under specific circumstances.