Utilize the input text as a context reference, choose the right relationship between 'Mary Barra' and 'General Motors' from the options.
Options: stock exchange, location of formation, employer, operator

DETROIT (Reuters) - General Motors Co (GM.N) Chief Executive Mary Barra said the automaker plans new efforts to capitalize on the connectivity built into its cars, expanding car sharing services, offering more autonomous driving features and enabling services through smartphone apps.
employer