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.
In the context of the input sentence, determine the relationship between 'Glencore' and 'mining'.
Options: director/manager, legal form, industry, operator