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: 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: Since 2002, the North East of the country has seen sectarian violence by Boko Haram, an Islamist movement that seeks to abolish the secular system of government and establish Sharia law. Nigerian President Goodluck Jonathan in May 2014 claimed that Boko Haram attacks have left at least 12,000 people dead and 8,000 people crippled. At the same time, neighbouring countries, Benin, Chad, Cameroon and Niger joined Nigeria in a united effort to combat Boko Haram in the aftermath of a world media highlighted kidnapping of 276 schoolgirls and the spread of Boko Haram attacks to these countries. Question: Who is the President of Nigeria?
Example Output: Goodluck Jonathan

Example Input: Passage: With the growing possibility of an Allied invasion in the Balkans, the Axis began to divert more resources to the destruction of the Partisans main force and its high command. This meant, among other things, a concerted German effort to capture Josip Broz Tito personally. On 25 May 1944, he managed to evade the Germans after the Raid on Drvar (Operation Rösselsprung), an airborne assault outside his Drvar headquarters in Bosnia. Question: What type of assault was there in Bosnia?
Example Output:
airborne