Which of the following correctly explains how selective incorporation contributed to the right to freedom of speech in the United States?

A. Selective incorporation required that states restrict speech that is controversial and unpopular.
B. Selective incorporation protected speech that creates a clear and present image.
C. Selective incorporation required that the right to freedom of speech be protected by state governments.
D. Selective incorporation required the national government to protect the right to freedom of speech

D. Selective incorporation required the national government to protect the right to freedom of speech

D. Selective incorporation required the national government to protect the right to freedom of speech.

To determine the correct explanation of how selective incorporation contributed to the right to freedom of speech in the United States, we need to understand what selective incorporation is and its impact on constitutional rights.

Selective incorporation is a legal doctrine that allows the Bill of Rights, which enumerates the fundamental rights of individuals, to be applied to the states through the Due Process Clause of the Fourteenth Amendment. Prior to selective incorporation, the Bill of Rights only applied to the federal government, not the states.

Option A suggests that selective incorporation required states to restrict speech that is controversial and unpopular. This statement is incorrect. The purpose of selective incorporation is to ensure the protection of individual rights from state infringement, and it does not require the restriction of controversial or unpopular speech.

Option B claims that selective incorporation protected speech that creates a clear and present danger. This statement is also incorrect. The clear and present danger test is a separate legal principle used to determine when speech can be limited to prevent harm, and it is not directly related to selective incorporation.

Option C states that selective incorporation required the right to freedom of speech to be protected by state governments. This statement is incorrect. Selective incorporation actually ensures that the federal Constitution and its amendments, including the First Amendment's protection of freedom of speech, apply to the states.

Option D correctly explains how selective incorporation contributed to the right to freedom of speech. By incorporating the First Amendment's protection of freedom of speech to the states, selective incorporation required the national government (specifically, the federal courts) to protect this right from infringement by state governments. This means that individuals are equally guaranteed the right to freedom of speech, regardless of whether they are dealing with state or federal authorities.

Therefore, the correct answer is D: Selective incorporation required the national government to protect the right to freedom of speech.