The answer is B: get key information.
When receiving a message it is of the utmost importance to capture the most important information in order to convey the message to the person that is destined to, so that in turn, he or she can follow up on the message´s information. When referring to a phone message, in particular, one should always be careful to capture the caller´s name, the person he or she is looking for, his or her purpose in calling, and, most importantly, the means to get back in touch with him or her.
