Utilize the input text as a context reference, choose the right relationship between 'Glencore' and 'mining' from the options.
Options: director/manager, operator, legal form, industry

CEC buys electricity from Zesco in bulk and sells it to mining companies including the local units of Vedanta Resources (Other OTC: VDNRF - news ) , Glencore (Xetra: A1JAGV - news ) and Vale.
industry