This task is about writing a correct answer for the reading comprehension task. Based on the information provided in a given passage, you should identify the shortest continuous text span from the passage that serves as an answer to the given question. Avoid answers that are incorrect or provides incomplete justification for the question.

Example Input: Passage: A virtual ISP (VISP) is an operation that purchases services from another ISP, sometimes called a wholesale ISP in this context, which allow the VISP's customers to access the Internet using services and infrastructure owned and operated by the wholesale ISP. VISPs resemble mobile virtual network operators and competitive local exchange carriers for voice communications. Question: What do VISPs resemble? 
Example Output: mobile virtual network operators

Example Input: Passage: In the mid-1950s, Frank Burnet, inspired by a suggestion made by Niels Jerne, formulated the clonal selection theory (CST) of immunity. On the basis of CST, Burnet developed a theory of how an immune response is triggered according to the self/nonself distinction: "self" constituents (constituents of the body) do not trigger destructive immune responses, while "nonself" entities (e.g., pathogens, an allograft) trigger a destructive immune response. The theory was later modified to reflect new discoveries regarding histocompatibility or the complex "two-signal" activation of T cells. The self/nonself theory of immunity and the self/nonself vocabulary have been criticized, but remain very influential. Question: What property of T cells caused modification of CST?
Example Output: the complex "two-signal" activation

Example Input: Passage: Public schools in Raleigh are operated by the Wake County Public School System. Observers have praised the Wake County Public School System for its innovative efforts to maintain a socially, economically and racial balanced system by using income as a prime factor in assigning students to schools. Raleigh is home to three magnet high schools and three high schools offering the International Baccalaureate program. There are four early college high schools in Raleigh. Raleigh also has two alternative high schools. Question: What is the school system praised for?
Example Output:
innovative efforts to maintain a socially, economically and racial balanced system