Here's the
official explanation provided by the GMAC for this question:
This sentence describes how three factors–traffic congestion, longer commuting trips, and the growing demand for housing–affect rural housing costs. The noun phrases denoting these three factors must be clearly distinguished to avoid implying that there is a growing demand for traffic congestion and for longer commuting trips as well as for housing. The main auxiliary verb
has or
have must agree with the singular or plural grammatical subject of the sentence.
Option A: The subject
The growing demand for housing, traffic congestion, and longer commuting trips, combined with the singular verb form
has, oddly indicates that there is a single, unified growing demand for housing, for traffic congestion, and for longer commuting trips--clearly not the intended meaning.
Option B: The plural compound subject
Traffic congestion, the growing demand for housing, and longer commuting trips does not agree with the singular verb form
has.
Option C: The plural compound subject
Longer commuting trips, traffic congestion, and the growing demand for housing does not agree with the singular verb form
has.
Option D: Correct. The plural compound subject
Traffic congestion, longer commuting trips, and the growing demand for housing agrees with the plural verb form
have. The compound subject is worded to unambiguously distinguish between the three factors it lists.
Option E: The singular grammatical subject here is simply
The growing demand for housing, which does not agree with the plural verb form
have. The parenthetical phrase
as well as traffic congestion and longer commuting times does not make the grammatical subject plural. The
as well as construction is unnecessarily wordy.
The correct answer is D.
Please note that I'm not the author of this explanation. I'm just posting it here since I believe it can help the community.