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?

　　Supernovas are not necessarily the most spectacular events that astronomers have occasion to observe.

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