Petulant is incorrect because it means that the volunteers were bad - tempered and volunteers usually are generous.
Clear is incorrect because it is stating that the volunteers were understanding when they were gathering over 100 boxes of food.
Both compassionate and resolute would be good answers for this question since resolute means determined and compassionate means a feeling of concern towards others. However, compassionate would be a better choice since the volunteers are putting all this effort in to help the physical needs (food) of the people in the local pantry.
have you tried looking the word up in the Dictionary? if that doesnt help much, you can guesstimate the word by searching it in the thesaurus! it will give you synonyms of the word.
