In this task, you are given a question and a context passage. You have to answer the question based on the given passage.
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Question: How does a chestnut tree form its heartwood?, Context: The term heartwood derives solely from its position and not from any vital importance to the tree. This is evidenced by the fact that a tree can thrive with its heart completely decayed. Some species begin to form heartwood very early in life, so having only a thin layer of live sapwood, while in others the change comes slowly. Thin sapwood is characteristic of such species as chestnut, black locust, mulberry, osage-orange, and sassafras, while in maple, ash, hickory, hackberry, beech, and pine, thick sapwood is the rule. Others never form heartwood.

Answer: the change comes slowly

Question: What makes Antarctic meteorites more desirable than meteorites from other continents?, Context: Meteorites from Antarctica are an important area of study of material formed early in the solar system; most are thought to come from asteroids, but some may have originated on larger planets. The first meteorite was found in 1912, and named the Adelie Land meteorite. In 1969, a Japanese expedition discovered nine meteorites. Most of these meteorites have fallen onto the ice sheet in the last million years. Motion of the ice sheet tends to concentrate the meteorites at blocking locations such as mountain ranges, with wind erosion bringing them to the surface after centuries beneath accumulated snowfall. Compared with meteorites collected in more temperate regions on Earth, the Antarctic meteorites are well-preserved.

Answer: Antarctic meteorites are well-preserved

Question: What did Madonna do four months after adopting Mercy James?, Context: Life with My Sister Madonna, a book by Madonna's brother Christopher, debuted at number two on The New York Times bestseller list. The book caused some friction between Madonna and her brother, because of the unsolicited publication. Problems also arose between Madonna and Ritchie, with the media reporting that they were on the verge of separation. Ultimately, Madonna filed for divorce from Ritchie, citing irreconcilable differences, which was finalized in December 2008. She decided to adopt from Malawi. The country's High Court initially approved the adoption of Chifundo "Mercy" James; however, the application was rejected because Madonna was not a resident of the country. Madonna appealed, and on June 12, 2009, the Supreme Court of Malawi granted Madonna the right to adopt Mercy James. She also released Celebration, her third greatest-hits album and final release with Warner. It contained the new songs "Celebration" and "Revolver" along with 34 hits spanning her career. Celebration reached number one in the UK, tying her with Elvis Presley as the solo act with most number one albums in the British chart history. She appeared at the 2009 MTV Video Music Awards on September 13, 2009, to speak in tribute to deceased pop star Michael Jackson.

Answer:
appeared at the 2009 MTV Video Music Awards