Utilize the input text as a context reference, choose the right relationship between 'Sergio Marchionne' and 'Fiat' from the options.
Options: operator, parent organization, employer, platform

Several months ago, Fiat Chrysler CEO Sergio Marchionne sent Barra an email saying he wanted the two companies to merge, a notion Barra has consistently said she and the company's board of directors are not interested in.
employer