What is the relationship between 'Glencore' and 'mining' in the context of the input sentence.
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