In this task, you are given a question and a context passage. You have to answer the question based on the given passage.

What does the S in "PBS" stand for?, Context: New York is also a major center for non-commercial educational media. The oldest public-access television channel in the United States is the Manhattan Neighborhood Network, founded in 1971. WNET is the city's major public television station and a primary source of national Public Broadcasting Service (PBS) television programming. WNYC, a public radio station owned by the city until 1997, has the largest public radio audience in the United States.
Service

What are the internal layer of pouches on an etioplast called?, Context: If angiosperm shoots are not exposed to the required light for chloroplast formation, proplastids may develop into an etioplast stage before becoming chloroplasts. An etioplast is a plastid that lacks chlorophyll, and has inner membrane invaginations that form a lattice of tubes in their stroma, called a prolamellar body. While etioplasts lack chlorophyll, they have a yellow chlorophyll precursor stocked. Within a few minutes of light exposure, the prolamellar body begins to reorganize into stacks of thylakoids, and chlorophyll starts to be produced. This process, where the etioplast becomes a chloroplast, takes several hours. Gymnosperms do not require light to form chloroplasts.
invaginations

What type of event is held to celebrate the Queen's Birthday?, Context: There is a variety of annual events, beginning with the relatively new New Year's Day Parade, fireworks display at the London Eye, the world's second largest street party, the Notting Hill Carnival is held during the late August Bank Holiday each year. Traditional parades include November's Lord Mayor's Show, a centuries-old event celebrating the annual appointment of a new Lord Mayor of the City of London with a procession along the streets of the City, and June's Trooping the Colour, a formal military pageant performed by regiments of the Commonwealth and British armies to celebrate the Queen's Official Birthday.

formal military pageant