One of the basic rules of computer security is to change your______regularly．

单项选择题A．支持性技术标准 B．质量管理和质量保证标准的选用和实施指南质量保证标准 D．质量管理标准 E．质量改进标准

单项选择题A sequence of any number of characters enclosed in the double queotes“”is called a character______.