Which of the following is more formal in tone?

A) Podcasts
B) Webinars
C) Memos
D) Letters
E) Proposals

E)Memos are brief printed documents traditionally used for the routine, day-to-day exchange of information within an organization. Letters are brief written messages sent to customers and other recipients outside the organization. Reports and proposals are usually longer than memos and letters, although both can be created in memo or letter format. These documents come in a variety of lengths, ranging from a few pages to several hundred, and are usually fairly formal in tone.