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.

Even though the Chinese government has persistently been trying to prevent further stock market losses by drawing the line around the 3,500 level for the Shanghai Stock Exchange Composite Index (SHCOMP), it is questionable whether it will continue to provide support in order to sustain this market level indefinitely, as it is proving to be a very expensive exercise.

Answer: operator: stock market, Stock Exchange