Utilize the input text as a context reference, choose the right relationship between stock market and stock exchange from the options. Options: 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.

Foreign market participants accounted for about 67 percent of stock market turnover on Tuesday, a senior Athens stock exchange official told Reuters.

Answer: operator