Answer:
The correct answer is B. Functional distance.
Step-by-step explanation:
Functional distance refers to the probability of people developing social interactions because of the living arrangements and the influence these have over them.
The architectural design makes certain individuals come more in contact with others and thus they can develop a social interaction more than with others.
In this case, the functional interaction occurs for couples who live at the foot of the stars or near mailboxes. It can be deduced that since the rest of the couples in the building have to come down the stairs or go to the mailboxes more often, they interact with the couples that live near these more than the rest of the individuals from the building.