Final answer:
The event that immediately precipitated the anti-French fever in 1798 was the expulsion of the American envoys from France. This led to outrage among the American people and the passage of the Alien and Sedition Acts.
Step-by-step explanation:
The event that immediately precipitated the anti-French fever that swept across the country in 1798 was C) The expulsion of the American envoys from France.
After Adams announced that the diplomatic mission had failed, his Republican critics accused him of acting too rashly because he favored Britain. Thomas Jefferson and other Republicans in Congress delayed any war-like measures and demanded that Adams share all the information he received from his ministers. The American people expressed outrage over the XYZ Affair and war fever gripped the nation. This event led to the passage of the controversial Alien and Sedition Acts.