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.

Passage: In 2004, a large share of natural gas reserves in Iran were untapped. The addition of new hydroelectric stations and the streamlining of conventional coal and oil-fired stations increased installed capacity to 33,000 megawatts. Of that amount, about 75% was based on natural gas, 18% on oil, and 7% on hydroelectric power. In 2004, Iran opened its first wind-powered and geothermal plants, and the first solar thermal plant is to come online in 2009. Iran is the third country in the world to have developed GTL technology. Question: How much of Iran's 33k megawatt installed capacity was based on oil?
18%

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?
the complex "two-signal" activation

Passage: The channel also broadcasts two movie blocks during the late evening hours each Sunday: "Silent Sunday Nights", which features silent films from the United States and abroad, usually in the latest restored version and often with new musical scores; and "TCM Imports" (which previously ran on Saturdays until the early 2000s[specify]), a weekly presentation of films originally released in foreign countries. TCM Underground which debuted in October 2006 is a Friday late night block which focuses on cult films, the block was originally hosted by rocker/filmmaker Rob Zombie until December 2006 (though as of 2014[update], it is the only regular film presentation block on the channel that does not have a host). Question: On what day is TCM Underground shown?
Friday