正确答案：(b) The grapevine and rumour are the two main types of informal communication.The grapevine is probably the best known type of informal communication. All organisations have a grapevine and it will thrive if there is lack of information and consequently employees will make assumptions about events. In addition, insecurity,gossip about issues and fellow employees, personal animosity between employees or managers or new information that has not yet reached the formal communication system, will all drive the grapevine.Rumours are the other main informal means of communication and are often active if there is a lack of formal communication.A rumour is inevitably a communication not based on verified facts and may therefore be true or false. Rumours travel quickly(often quicker than both the formal system and the grapevine) and can influence those who hear them and cause confusion,especially if bad news is the basis of the rumour. Managers must ensure that the formal communication system is such that rumours can be stopped, especially since they can have a serious negative effect on employees.