Final answer:
The specific symbol for a dryer heat high limit switch can vary depending on the technical documentation or manufacturer. Without the context of a specific schematic, it's not possible to accurately identify whether symbol a. 1, b. 2, c. 3, or d. 7 is correct.
Step-by-step explanation:
The symbol that represents a dryer heat high limit switch typically falls within the domain of technical documentation and electrical schematics, and it's not generally standardized across all documents or manufacturers. Symbols in technical diagrams can vary, but a common symbol for a high limit switch may be a line with a semicircle at the end, often accompanied by text or numbers that identify it as a high limit switch. However, to answer this question unequivocally, one would need the context of a specific schematic or set of conventions; for instance, in option d. 7 could be the symbol in the provided context. Unfortunately, without seeing the specific diagram or reference material from which the question is derived, it's not possible to provide a definitive answer to which symbol, a. 1, b. 2, c. 3, or d. 7, represents a dryer heat high limit switch.