Section4.2 – Test Coverage Criteria for AI Modelsof the ISTQB CT-AI syllabus describes neural network–specific coverage methods. Among the techniques,threshold coverageis explicitly noted asadaptable, meaning testers may choose different thresholds to determine whether neuron activation is considered “covered.” This flexibility makes threshold coverage adjustable to the model architecture, problem domain, and required test thoroughness.

Options A and B (Sign–Sign and Sign–Change coverage) are more rigid structural criteria and are not described as adaptable within the syllabus. They focus on sign patterns of neuron activations and do not allow altering thresholds. Option D, neuron coverage, measures the proportion of neurons activated at least once. Although simple, it is not defined as an adaptable criterion. Its limitations are documented: it provides shallow insight and too easily achieves high coverage.

Onlythreshold coverageallows testers to adjust activation thresholds for more refined coverage measurement, makingOption Cthe correct choice.