The survey items are divided into background information, health status items and questionnaire survey items. The health status item includes various oral diseases, which is the main content of oral health survey and depends on the purpose of the survey. The most commonly used investigation items are dental caries, periodontal disease, dentition, etc. Others such as dental fluorosis, enamel hypoplasia, oral mucosa, temporomandibular joint, etc. , excluding soft scale and plaque, so this question chooses C.