What type of instruction uses a mathematical expression to perform conversion operations on an input source?

The correct answer is based on the characteristics of the CPT instruction, which stands for Calculate. This instruction is designed specifically to evaluate mathematical expressions that can involve multiple types of operations, such as addition, subtraction, multiplication, and division, in a single step.

The CPT instruction allows the user to perform complex conversions and computations by enabling the use of formulas or expressions to transform input data into a desired output. This is particularly useful in control systems where calculations may be necessary to interact with process variables effectively.

In contrast, the other instructions listed—MUL, ADD, and SUB—are specific to individual operations. MUL is strictly for multiplication, ADD for addition, and SUB for subtraction. They do not provide the flexibility of handling complex expressions or multiple operations simultaneously, which is why they would not be classified as instructions that perform conversion operations on an input source in the same comprehensive manner as the CPT instruction.