Final answer:
Antonio should revise the slide by including a paragraph of text explaining the research problem to make the purpose of his research clearer to the audience.
Step-by-step explanation:
Antonio can revise the slide by making the following improvement to ensure the purpose of his research problem is clear:
Option D: Include a paragraph of text explaining the research problem.
By adding a concise paragraph, Antonio can clearly articulate the research problem which is a lack of parental guidance contributing to excessive cell phone usage among teens. This textual explanation will provide the necessary context and support the image, making the presentation more effective. While other options like enlarging the text or adding animations may provide aesthetic enhancements, a paragraph will add depth to the understanding of the research problem and his findings.