选择题：Until the early 20th century failure to bear a son was grounds for divorce.South

Until the early 20th century failure to bear a son was grounds for divorce.South Koreans greatly preferred boys,who could not only support their parents financially but also carry out ancestral rites.When ultrasound technology became widespread in the 1980s,many South Koreans used it to detect female femses and then have them aborted.Sex ratios became skewed.In response to these trends the South Korean government made it illegal for doctors to reveal the sex of a fetus,Following the Asian financial crisis of 1997,many women took part-time jobs to supplement the family income.Parents noticed,and began to invest more heavily in educating girls.In 2015 three-quarters of South Korean female secondary-schoolers went to university,compared with two-thirds of their male peers.Since 2009 expectant parents have been allowed to know the sex of their baby after 32 weeks'gestation.Many will have found out before,from doctors who trust that parents'attitudes have changed.