The correct answer is Subject
Step-by-step explanation:
In grammar, there are different elements that can be part of a sentence this includes the subject which is the agent that performs or is related to the main action or verb; the verb that is the action of the sentence; the direct object that is the entity affected by the action and the object of a preposition that refers to words that follow a preposition such as it, with, from, etc and that complete the meaning of the preposition.
In the case of the sentence "During June and July, when the hillsides are streaked with color, wildflower enthusiasts are always delighted" in this sentence the subject and verb are not presented at the beginning but at the end as the main action is "are" the complement is "always delighted" and the subject is "wildflower enthusiasts" who are the people related to the main actions, while the rest of the information work expand the meaning of "always delighted". Therefore, the words "wildflower enthusiasts" is the subject or the agent that is related to the main action rather than an object.