The correct answer is C. Working memory
Step-by-step explanation:
The term working memory (synonym for short-term memory) refers to the memory system that allows us to remember and retain information for a short time. This type of memory is used daily for example, you use it to remember what to buy in the supermarket or what you did yesterday. Additionally, it differs from long-term memory than stores information for a long time, and from sensory memory that is related to the senses.
According to this, Abdul's task requires mainly working memory because he needs to remember the number just for a short time while he dials the number, but once he completes the task he does not need to remember it, also this information is not related to senses and therefore it is the working memory the type of cognitive system involved.