The answer is letter D. subject: dumpster; verb: overflowed.
Explanation:
A subject is most commonly a noun that refers to the topic of the sentence (what the sentence is about) or even the thing or person that performed the action described by the verb.
The verb is a word that expresses a state of being or an action.
In the structure we are analyzing here, the noun "dumpster" performs the action of overflowing. Thus, "dumpster" is the subject and "overflowed" is the verb.
A well-organised essay will have a clear definite structure. The organisation is dependent on clear and decisive decisions. The best option out of all the choices appears to be D.