To make a long-distance call, tom has to dial an unfamiliar phone number. he looks up the number but may have trouble retaining it. this best illustrates the limited capacity of memory.

The correct answer is short-term memory.

Short-term memory (STM) refers to our ability and capacity for retaining a small amount of information for a short period of time. Remembering an unfamiliar phone number entails the use of our STM. However, a phone number is difficult to retain in our STM because STM has a digit span of approximately seven units. This means that our STM can hold around seven digits of a phone number and not all (10+) of them.