The primary and most critical purpose of coding standards is to enforce a uniform, consistent style and structure across a codebase. This consistency is paramount for improving the long-term maintainability of the software. When code is easy to read and understand, developers can more efficiently and safely debug, modify, and enhance it over its lifecycle. While other benefits may exist, they are secondary to or a direct result of improved maintainability.

B. Coding standards should educate the programmer: While following standards can be a learning experience, their primary function is to ensure code quality and consistency, not to serve as a pedagogical tool.

C. Coding standards should increase the efficiency of the programmer: This is a potential long-term benefit derived from increased readability and maintainability, but it is not the primary goal. Initially, enforcing standards can even slow programmers down.

D. Coding standards should increase the efficiency of the source code: Coding standards focus on human-readable source code, not the performance of the compiled, executable code. Code performance is the responsibility of the compiler and the algorithm design.

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1. ISTQB® Certified Tester Foundation Level Syllabus 2018 (v3.1): In section 3.2.2, "Static analysis by tools," the syllabus states that static analysis can "improve the maintainability, portability and testability of the code" by checking for compliance with coding standards. This directly links coding standards to the goal of maintainability.

2. University of Texas at Austin, Department of Computer Science Courseware: In the lecture notes for course CS 373: Software Engineering, it is explicitly stated: "The main purpose of a coding standard is to promote maintainability of the code. Other developers will be able to read and understand the code more easily." (Downing, G., "Coding Standard," CS 373, University of Texas at Austin).

3. Lanza, M., & Marinescu, R. (2006). Object-Oriented Metrics in Practice. Springer. In Chapter 2, "No Code is an Island," the authors discuss how coding conventions are crucial for team collaboration and future maintenance. They state, "The problem is that code is not only written, but also read, and this is usually done by other people long after the original author has left... This is why coding conventions are so important." This emphasizes the role of standards in long-term readability and maintainability.