Question: On which stock exchange does the makers of Panadol night have a primary listing?
Context: Philadelphia Stock Exchange (PHLX), now known as NASDAQ OMX PHLX, is the oldest stock exchange in the United States.  It is now owned by The NASDAQ OMX Group.  Founded in 1790, the exchange was originally named the Board of Brokers of Philadelphia, also referred to as the Philadelphia Board of Brokers.  In 1875, the Board of Brokers changed its name to the Philadelphia Stock Exchange.  The exchange merged with the Baltimore Stock Exchange in 1949 and was named the Philadelphia-Baltimore Stock Exchange.  It merged with the Washington Stock Exchange in 1954, becoming known as the Philadelphia-Baltimore-Washington Stock Exchange (often abbreviated as PBW).  In 1969, the exchange acquired the Pittsburgh Stock Exchange.  In 2007, PHLX was purchased by NASDAQ for $652 million. CGI Group Inc. (Consultants to Government and Industries), more commonly known as CGI, is a Canadian global information technology (IT) consulting, systems integration, outsourcing, and solutions company headquartered in Montreal, Quebec, Canada.  Founded in 1976 by Serge Godin and André Imbeau as an IT consulting firm, the company soon began branching into new markets and acquiring other companies.  CGI went public in 1986 with a primary listing on the Toronto Stock Exchange.  CGI is also a constituent of the S&P/TSX 60, and has a secondary listing on the New York Stock Exchange.  After almost doubling in size with the 1998 acquisition of Bell Sygma, CGI acquired IMRGlobal in 2001 for $438 million, which added "global delivery options" for CGI.  Other significant purchases include American Management Systems (AMS) for $858 million in 2004, which grew CGI's presence in the United States, Europe and Australia and led to the formation of the CGI Federal division. The company has a primary listing on the London Stock Exchange and is a constituent of the FTSE 100 Index.  As of August 2016 it had a market capitalisation of £81 billion (around $107 billion), the fourth largest on the London Stock Exchange.  It has a secondary listing on the New York Stock Exchange. The FTSE 350 Index index is a market capitalization weighted stock market index incorporating the largest 350 companies by capitalization which have their primary listing on the London Stock Exchange.  It is a combination of the FTSE 100 Index of the largest 100 companies and the FTSE 250 Index of the next largest 250.  The index is maintained by FTSE Russell, a subsidiary of the London Stock Exchange Group.  See the articles about those indices for lists of the constituents of the FTSE 350. An unlisted public company, or a publicly unlisted company, is a public company, which is a company that can have an unlimited number of shareholders to raise capital for any commercial venture, but which is not listed on any stock exchange.  A company may not be listed on a stock exchange for a number of reasons, including because it is too small to qualify for a stock exchange listing, does not seek public investors, or there are too few shareholders for a listing.  Each stock exchange has its own listing requirements.  Unlisted public companies tend to be larger than companies limited by guarantee. Pearson PLC is a British multinational publishing and education company headquartered in London.  It was founded as a construction business in the 1840s.  It shut down its construction activities in the 1920s and switched to publishing.  It is the largest education company and the largest book publisher in the world.  Pearson has a primary listing on the London Stock Exchange and is a constituent of the FTSE 100 Index.  It has a secondary listing on the New York Stock Exchange in the form of American Depository Receipts. Oil and Gas Development Company Limited commonly known as OGDCL is a Pakistani multinational oil and gas company.  It has a primary listing on the Pakistan Stock Exchange, and secondary listing on the London Stock Exchange.  Established in 1961 by the Government of Pakistan, it was turned into a public listed company on 23 October 1997.  Today it is involved in exploring, drilling, refining and selling oil and gas in Pakistan.  It is the market leader in terms of reserves, production and acreage.  It is based on Jinnah Avenue, Blue Area in Islamabad, with the Government of Pakistan holding 74% stake in the company.  Rest are held by private investors.  In 2013, it has revenue of Rs.  223.365 billion and profit before tax soaring at Rs.  90.777 billion. Panadol night is a GlaxoSmithKline painkiller intended for use at night.  It consists of 500 milligrams of paracetamol, 25 milligrams of diphenhydramine hydrochloride (a sedating antihistamine) and other "non-hazardous ingredients" It is sold in Australia, Cyprus United Kingdom, Ireland, New Zealand and the Middle East.  It became available as an over the counter medication in the UK in 1996. Cairn Energy PLC is one of Europe's leading independent oil and gas exploration and development companies and is listed on the London Stock Exchange.  Cairn has discovered and developed oil and gas reserves in a variety of locations around the world.  Cairn Energy has a primary listing on the London Stock Exchange and is a constituent of the FTSE 250 Index. CRH plc is the parent company for an international group of diversified building materials businesses which are engaged in the manufacture and supply of a wide range of building materials and in the operation of builders’ merchanting and DIY stores.  The company is incorporated and domiciled in Ireland where it ranks as the largest Irish company.  CRH has a primary listing on the London Stock Exchange and is a constituent of the FTSE 100 Index.  It has secondary listings on the Irish Stock Exchange (where it is a constituent of the ISEQ 20) and New York Stock Exchange.
Answer: the London Stock Exchange