Question

when a new street is being laid out, each utility is given a specific location according to a master plan. the sewer and drain are located farthest down and approximately under the center of the street. above them is the steam system, which needs at least six feet of soil above it because of the high temperatures it produces. closer both to the surface and to the sides of the street are the water and gas pipes, while just two feet below the surface are the electric and telephone cables. in an area requiring all these utilities, however, it is very rare that a new street can conform completely to this ideal plan. most underground systems have grown gradually and randomly over many years and since the problem is usually to increase or replace what already exists, it is often necessary to squeeze things in wherever they will fit. the plan is difficult to

understand

connect

illustrate

maintain

Explanation:

The text states that most underground systems have grown gradually and randomly, and when increasing or replacing existing utilities, it's often necessary to "squeeze things in". This implies that it's hard to keep or "maintain" the ideal master - plan.

Answer:

D. maintain