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.
Take context from the input text and decide on the accurate relationship between 'Glencore' and 'mining' from the options provided.
Options: legal form, industry, director/manager, operator