Explanation:

When programmers write computer programs using a high-level programming language, the text they write is called source code. This code is human-readable and understandable, allowing programmers to develop, debug, and maintain software. It then needs to be compiled or interpreted into machine code for the computer to execute. Option (c) Source code is the correct term. Option (a) Cache is a high-speed data storage layer. Option (b) Instruction set is a collection of low-level instructions a CPU understands. Option (d) Word size refers to the number of bits a CPU processes at once. None of these relate to the human-readable form of a program.