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In extended families, the older membem' opinions are respected, and the youngest membem are loved and taken good care of by all．China's constitution stipulates that grown-up children are duty-bound to support their parents．In the cities, couples who do not live with their aged parents give the latter living allowances and help them with the house chores．In the countryside, though quite a number of extended families have dissolved, many married sons and their families continue to live In the same courtyard with their parents．To them, breaking up the extended family means cooking their meals separately．Married sons most often have their houses built near their parents' home, making it convenient for parents and children to help and visit each other as before.
A．He started to work on refrigeration. B．He became a professor of Mathematics. C．He fell in love with Natasha Willoughby. D．He distinguished himself in low temperature physics.