Everyman is both a morality play and an allegory.
It is a morality play because it teaches a lesson about life and the best way to live.
It is an allegory because each character represents an abstract idea. For example, "Goods" literally represents material things -- therefore it is not surprising that material goods are no help to Everyman on his journey.
That is not non-assertive behavior. Non assertive behavior is when you are feeling dishonest or indirect emotionally.
The word that a poet would most likely use as a symbol of violence is, option C. Thunder. A thunder is characterized by its strong, loud, striking and explosive sound, which is why it is most likely related to violence in which they are somewhat similar in characteristics.
A dependent clause is a clause that cannot stand on its own and make sense which is why it requires an independent clause to give it meaning.