A. Select email from student where email!=null B. Select email from student where emailnotisnull C. Select email from student where email<>null D. Select email from student where emailisnotnull
A. 不必衣帽整洁,既右执行技术操作 B. 应衣帽整洁,既右执行技术 C. 应衣帽整洁,严格执行无菌技术操作规程 D. 不必衣帽整洁,只要严格执行无菌技术操作规程既可