Final answer:
The next step is to write the body of the essay, where you will present and develop your arguments using evidence from your research.
Step-by-step explanation:
The next step in expanding the outline about the American Dream into an argumentative research essay is to d) Write the body of the essay.
The body of the essay is where you will present and develop your arguments and provide evidence from your research to support your claims. Each body paragraph should focus on a specific point or argument and include in-text citations to credit the sources you used. Make sure to analyze and evaluate the information as you present it to further strengthen your position.