The correct answer is option 'C', the Diagnostic Mathematical Skill Test.

Explanation:
The Diagnostic Mathematical Skill Test is used to find errors committed by students during mathematical operations. This test is designed to assess the student's understanding and application of mathematical concepts and procedures. It helps identify specific areas where the student may be making mistakes or struggling with certain concepts.

The purpose of the Diagnostic Mathematical Skill Test is to diagnose the student's mathematical abilities and identify any gaps in their knowledge or understanding. It can help determine the specific areas that need improvement and provide insights into the student's strengths and weaknesses in mathematical operations.

By administering this test, educators can identify common errors or misconceptions made by students, such as calculation errors, incorrect application of formulas or procedures, misunderstanding of mathematical concepts, or lack of problem-solving skills. This information can be used to guide instruction and provide targeted remediation for individual students.

The Diagnostic Mathematical Skill Test typically includes a variety of mathematical problems that cover different topics and skills. It may include questions related to arithmetic operations (addition, subtraction, multiplication, division), fractions, decimals, percentages, algebraic equations, geometry, and more. The test may be administered in written or digital format, depending on the educational setting.

Overall, the Diagnostic Mathematical Skill Test is a valuable tool for educators to assess and address the specific errors and misconceptions made by students during mathematical operations. It helps identify areas for improvement and guides instruction to ensure students develop a strong foundation in mathematical skills.