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 closure of the Athens Stock Exchange since Monday has made it impossible for managers to ascertain exactly how far the value of shares in bluechip Greek companies such as Alpha Bank and Hellenic Telecommunications might have fallen since the country fell deeper into crisis.
headquarters_location: Alpha Bank, Athens