正解:A
Informal communication is a type of communication that is casual, spontaneous, and unstructured. It does not follow any predefined rules, protocols, or formats. Examples of informal communication include email, phone calls, conversations in the hallway, and impromptu meetings12. The sponsor is using informal communication to communicate with the team, as these methods are convenient, flexible, and personal. However, informal communication may also have some drawbacks, such as lack of documentation, inconsistency, and potential for misunderstanding3. Therefore, the sponsor should also use formal communication when necessary, such as for official reports, contracts, and presentations4.