The correct answer is C. 1900.
During the 1900 Census in the United States, it was revealed that approximately two million children were working across the country. This historical event shed light on the issue of child labor and played a significant role in the development of labor laws and regulations to protect the rights of children and ensure their education and well-being.
By selecting option C, you are acknowledging the significance of the 1900 Census in highlighting the widespread issue of child labor and the need for reforms to improve the conditions of young workers in the United States.
