Final answer:
The key difference between authoritarian and U.S. political institutions is the protection of freedoms like speech and assembly. The First Amendment safeguards these freedoms in the U.S., and citizens can protest, take legal action, or vote to defend their rights if they are threatened.
Step-by-step explanation:
A. A notable difference between the political institutions of your friend's home country, which is run by an authoritarian government, and the United States is that while the former likely suppresses all opposition to the ruling regime, the latter is based on a democratic system where freedom of speech and political pluralism are legally upheld and practiced.
B. One provision in the government of the United States that protects your friend's freedoms is the First Amendment which guarantees fundamental liberties such as freedom of speech, religion, press, assembly, and the right to petition the government for a redress of grievances.
C. If the U.S. government denied those freedoms, citizens could take several actions, such as exercising their right to peaceful protest, taking legal action through the courts, engaging in civil disobedience, or using the electoral process to vote for representatives who will uphold and defend their rights. Furthermore, the free press can raise awareness and advocate for restoration and protection of civil liberties.