By the end of the twentieth century, how many people traveled by air each year? (1 point)

11.3 million people
18.1 million people
• 5 billion people
• 1.8 billion people

The options given do not accurately represent the correct answer as they are all much lower than the actual number. By the end of the twentieth century, the number of people traveling by air each year was significantly higher. It is estimated that approximately 1.8 billion people traveled by air by the end of the twentieth century.