The circumstellar cloud surrounding IRC+10216 consists of material expelled from that star.

　　 The age of a star is equal to that of its circumstellar cloud.

　　 The rate at which IRC+10216 loses mass varies significantly from year to year.

　　 Stars with a mass greater than 6 M⊙ lose mass at a rate faster than stars with a mass less than 6 M⊙ do.

　　25. According to information provided by the passage, which of the following stars would astronomers most likely describe as a planetary nebula?

　　 A star that began its life with a mass of 5.5 M⊙, has exhausted its nuclear fuel, and has a core that is visible to astronomers

　　 A star that began its life with a mass of 6 M⊙, lost mass at a rate of 1 M⊙ per 10,000 years, and exhausted its nuclear fuel in 40,000 years

　　 A star that has exhausted its nuclear fuel, has a mass of 1.2 M⊙, and is surrounded by a circumstellar cloud that obscures its core from view

　　 A star that began its life with a mass greater than 6 M⊙, has just recently exhausted its nuclear fuel, and is in the process of releasing massive amounts of gravitational energy

　　 A star that began its life with a mass of 5.5 M⊙, has yet to exhaust its nuclear fuel, and exhibits a rate of mass loss similar to that of IRC+10216

　　26. Which of the following statements would be most likely to follow the last sentence of the passage?

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