Which of the following countries is the largest by population?

A. China
B. Russia
C. United States
D. Brazil

To find out which of the following countries is the largest by population among China, Russia, United States, and Brazil, we can compare the population numbers of each country.

One way to obtain accurate and up-to-date population data is by referring to reliable sources such as the World Bank, the United Nations, or the Central Intelligence Agency (CIA) World Factbook. These sources regularly update their data to provide the most accurate information.

Alternatively, you can also use a search engine to look up the respective population numbers for each country.

Now, let's briefly discuss the population of each country:

A. China: China is the most populous country in the world, with a population of approximately 1.4 billion people (as of 2021).

B. Russia: Russia has a significant population, but it is not as large as China. As of 2021, the population of Russia is around 145 million people.

C. United States: The United States has a high population, but it is still smaller than China's. As of 2021, the population of the United States is approximately 331 million people.

D. Brazil: Brazil also has a substantial population, but it is not as large as China's. As of 2021, the population of Brazil is around 213 million people.

Based on the population numbers provided, it is clear that China has the largest population among the given countries. Therefore, the correct answer is A. China.