Instructions: This task is about writing a correct answer for the reading comprehension task. Based on the information provided in a given passage, you should identify the shortest continuous text span from the passage that serves as an answer to the given question. Avoid answers that are incorrect or provides incomplete justification for the question.
Input: Passage: Thirty-nine Native American tribal governments are based in Oklahoma, each holding limited powers within designated areas. While Indian reservations typical in most of the United States are not present in Oklahoma, tribal governments hold land granted during the Indian Territory era, but with limited jurisdiction and no control over state governing bodies such as municipalities and counties. Tribal governments are recognized by the United States as quasi-sovereign entities with executive, judicial, and legislative powers over tribal members and functions, but are subject to the authority of the United States Congress to revoke or withhold certain powers. The tribal governments are required to submit a constitution and any subsequent amendments to the United States Congress for approval. Question: Who must approve tribal constitutions?
Output:
the United States Congress