Given the input sentence, please extract the subject and object containing a certain relation in the sentence according to the following relation types, in the format of "relation1: word1, word2; relation2: word3, word4". Relations include: product/material produced; manufacturer; distributed by; industry; position held; original broadcaster; owned by; founded by; distribution format; headquarters location; stock exchange; currency; parent organization; chief executive officer; director/manager; owner of; operator; member of; employer; chairperson; platform; subsidiary; legal form; publisher; developer; brand; business division; location of formation; creator.

The steady and sharp fall in coal prices has knocked down shares of big mining companies like BHP Billiton (NYSE: BBL - news ) , Glencore (Xetra: A1JAGV - news ) and Rio Tinto (LSE: RIO.L - news ) , and it has seen many financers exit the sector.

Answer: industry: Glencore, mining