With reference to digital communication, which of the following statements A-D are true?

A. A Radio broadcast is an example of automatic type of transmission mode.

B. A Keyboard communicating with a computer is an example of simplex type of transmission mode.

C. Walkie-Talkies operate on half-duplex transmission mode.

D. Telephone calls are an example of full-duplex transmission mode.

Choose the most appropriate answer from the options given below: