Final answer:
The sentence should be completed with "has become" to express an occurrence that started in the past and continues in the present, employing the present perfect tense.
Step-by-step explanation:
The correct answer to fill in the blank for the sentence "Rockwell's art __________ an iconic symbol to many Americans" with a verb that expresses an occurrence that began in the past and continues presently is "has become." This verb choice clearly indicates that Rockwell's art became an iconic symbol at some point in the past and continues to be so in the present.
When trying to convey something that started in the past and is still relevant or happening in the present, the present perfect tense is generally used. The present perfect tense is formed with the auxiliary verb "has" (for singular subjects) or "have" (for plural subjects), followed by the past participle of the main verb, in this case, "become." Therefore, the completed sentence reads: "Rockwell's art has become an iconic symbol to many Americans."
Using an understanding of verb tenses, specifically the present perfect, is crucial in maintaining consistency and clarity in writing. It ensures that the readers understand the timeline and the ongoing relevance of the subject being discussed. The usage of present perfect tense provides the readers with a sense of continuity from past to present.