Why do foreign couples always have the same last name?

According to foreign customs, a woman married to her husband's last name, like the typical continental countries such as France, Germany, including the United States, Britain and other Western countries, so far are women with their husband's last name. For example, U.S. Senator Hillary Clinton, the current U.S. Secretary of State, is with her husband's last name. There is of course selectivity, but most people change it, especially the typical aristocrats. China, on the other hand, has made great improvements in this area and has basically abolished it, except for different customs most of them don't have to

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