Answer: The grapevine communication
Explanation: This type of communication is the most common form of informal communication at work, i.e in an organisation. It is, in fact, the simplest or purest form of communication, it is a dialogue that does not have some prescribed structural form at the level of, say, a job with a manager, etc., so it is not an official conversation with certain rules and procedures. As this is an informal and simple form of communication for everyone with everyone, this kind of communication is spreading rapidly throughout the organisation and most likely at its speed with which such communication will spread to all employees. Clearly, news like this is spreading very quickly, informally and effectively.