Question: Who are the four key resident companies of the Sydney Opera House?
About the article "Sydney Opera House", section "Abstract".

Candidate passages:
The Sydney Opera House is a multi-venue performing arts centre in Sydney, New South Wales, Australia.
Situated on Bennelong Point in Sydney Harbour, close to the Sydney Harbour Bridge, the facility is adjacent to the Sydney central business district and the Royal Botanic Gardens, between Sydney and Farm Coves.
Designed by Danish architect Jørn Utzon, the facility formally opened on 20 October 1973 after a gestation beginning with Utzon's 1957 selection as winner of an international design competition.
The NSW Government, led by Premier Joseph Cahill, authorised work to begin in 1958, with Utzon directing construction.
The government's decision to build Utzon's design is often overshadowed by circumstances that followed, including cost and scheduling overruns as well as the architect's ultimate resignation.
Though its name suggests a single venue, the project comprises multiple performance venues which together are among the busiest performing arts centres in the world — hosting over 1,500 performances each year attended by some 1.2 million people.
The venues produce and present a wide range of in-house productions and accommodate numerous performing arts companies, including four key resident companies: Opera Australia, The Australian Ballet, the Sydney Theatre Company and the Sydney Symphony Orchestra.
As one of the most popular visitor attractions in Australia, more than seven million people visit the site each year, with 300,000 people participating annually in a guided tour of the facility.
Identified as one of the 20th century's most distinctive buildings and one of the most famous performing arts centres in the world, the facility is managed by the Sydney Opera House Trust, under the auspices of the New South Wales Ministry of the Arts.
The Sydney Opera House became a UNESCO World Heritage Site on 28 June 2007.
The National Opera Studio in London, England was established by the Arts Council as a link between the music colleges and the six main UK opera companies.
It was resident at Morley College in Lambeth until 2003, when it gained use for the first time of its own dedicated premises in Chapel Yard, Wandsworth.
Its director is the soprano Kathryn Harries, who succeeded Donald Maxwell at the start of 2009, its Head of Music is Mark Shanahan.
It is responsible for the training of approximately twelve singers each academic year, as well as three piano repetiteurs.
Its funding comes in part from the six main UK opera companies – Royal Opera House, English National Opera, Welsh National Opera, Scottish Opera, Opera North and the Glyndebourne Festival Opera.
Representatives from each company sit on the final audition panel for selection of each year's intake.
The one-year course usually includes residencies at two of the national opera companies, as well as four opera scene performances in London throughout the year. 
Macquarie Street is the easternmost street of Sydney's central business district.
Macquarie Street extends from Hyde Park at its southern end to the Sydney Opera House at its north.
Apart from connecting these two major landmarks, the key government institutions of the state of New South Wales are all located beside this street. 
The complex has four resident companies:  Los Angeles Philharmonic  Los Angeles Opera  Los Angeles Master Chorale  Center Theatre Group  
Olivia Newton-John and the Sydney Symphony: Live at the Sydney Opera House is a HD video (16:9) released in 2008 for a tour of four concerts at the Sydney Opera House of singer Olivia Newton-John.
The show was done in March 2006 with her band and Sydney Symphony conducted by Rick King.
Produced by Olivia's Gaia Productions.