Answer:
The word that best completes the sentence is the following one:
friendly.
Explanation:
If the audience is passive, it means all you can get from it is apathy.
If the audience is neutral, it is formed by people who hear you speak without taking any sides. In other words, everybody stays on the fence.
If the audience is hostile, it means all that is expressed by it is anger.
Therefore, a friendly audience is likely to be more sympathetic, since the people in that audience are able to express friendliness, which is a humane feature. If people can be humane, they can certainly be sympathetic.