Immigrants, China citizens emigrate or permanently settle in a certain area of China. According to the above definition, the following are immigrants ().

70.d [Solution] Immigration means that our citizens move to a foreign country or a certain area of our country to live permanently. Only item d meets the definition requirements, and options a and b are temporary business trips abroad, which do not meet the conditions of permanent residence; Option C refers to China citizens who have returned from studying abroad and have not emigrated or permanently resided in a certain area in China, which does not meet the definition. So choose D.