Final answer:
In 1900, Mongolia was part of the Qing Empire, which means it was under Chinese control. The correct answer is b. China. Mongolia declared independence in 1911 and later became a de facto protectorate of the Soviet Union.
Step-by-step explanation:
In 1900, Mongolia was part of the Qing Empire, which indicates that it was under Chinese control at that time. Therefore, the answer to the question 'What country was Mongolia part of in 1900?' is b. China.
Historically, this period was before the existence of the Soviet Union, which was established after the Russian Revolution of 1917. It was also long before North Korea and South Korea became independent nations, which only occurred following the end of World War II. Additionally, Japan, while active in the region, did not have control over Mongolia.
To provide more context related to the era and region, it's worth noting that after the Boxer Rebellion, which saw an uprising against foreign influence in China, there were movements in East Asia where powers like Russia and Japan were vying for influence, with Japan occupying Korea and Russia focusing on Manchuria. However, Mongolia remained under Chinese sway until it declared independence in 1911, eventually becoming a de facto protectorate of the Soviet Union in the early 20th century.