单项选择题
Medium survey should be carried out （） times during the valid period of the certificate.
单项选择题 The first survey has two situations, one is changing （） survey, the another is making survey.
单项选择题 In the first survey, （） compiles the survey report and fills in certificate.
单项选择题 （） is/are the legal survey institution(s) that stated by PRC.
