instruction: Based on this passage, in what field did Raisa earn her PhD?
context: In June 1955, Gorbachev graduated with a distinction; his final paper had been on the advantages of "socialist democracy" (the Soviet political system) over "bourgeois democracy" (liberal democracy). He was subsequently assigned to the Soviet Procurator's office, which was then focusing on the rehabilitation of the innocent victims of Stalin's purges, but found that they had no work for him. He was then offered a place on an MSU graduate course specializing in kolkhoz law, but declined. He had wanted to remain in Moscow, where Raisa was enrolled in a PhD program, but instead gained employment in Stavropol; Raisa abandoned her studies to join him there.
response: Based on this passage, Raisa did not earn a PhD. She abandoned her graduate studies in Moscow in order to join Gorbachev in Stavropol.