1) Explanation

Let's break down the sentence to understand the context and the meaning required for the blank:
- "Public transportation offers an environmentally friendly and cost-efficient alternative to driving, particularly in crowded urban areas; however,..."
- This sets up a contrast. Public transportation has positive aspects (environmentally friendly, cost-efficient). The "however" indicates that the blank will describe a negative aspect that makes it "undesirable."
- "...the $\qquad$ schedules of the buses and trains makes them an undesirable option to many commuters."
- The blank describes the nature of the "schedules" that would make public transportation undesirable. What kind of schedules would deter commuters? Schedules that are unreliable, unpredictable, or constantly changing.

Therefore, the blank needs words that mean unreliable, unpredictable, or lacking consistency.
Let's evaluate the given options:
- A. malevolent: Having or showing a wish to do evil to others. This describes a malicious intent, which doesn't apply to schedules.
- B. saturnine: (Of a person or their manner) slow and gloomy. This describes a mood, not a schedule.
- C. viscous: Having a thick, sticky consistency between solid and liquid. This describes a physical property, not a schedule.
- D. inconsistent: Not staying the same throughout; erratic or contradictory. This perfectly describes schedules that are unreliable or unpredictable, making them undesirable for commuters.
- E. fluctuant: Tending to fluctuate; wavering. This is a direct synonym for inconsistent, implying changes and unreliability in schedules.
- F. vicious: Deliberately cruel or violent; (of a thing) dangerously aggressive. This describes a harmful quality, but not in the context of schedules.

Conclusion:

The "however" signals a negative aspect of public transportation that offsets its benefits. Unreliable or unpredictable schedules would certainly make public transport undesirable. Both "inconsistent" and "fluctuant" convey this meaning.

The final answer is $\(\mathrm{D}, \mathrm{E}\)$.