The data in the question reflects many factors such as national transportation, economic employment and so on. The developed economy in eastern China has attracted a large number of rugged people from the central and western regions to work, and the number of people working in Beijing is far greater than that of Beijingers who have moved abroad. The reason why the population moved to Beijing this time is mainly because Beijing is one of the largest transportation hubs, and there are many people transiting in Beijing.

Therefore, choose: d.