Which of the following statements is true in the context of the formation of stars from the interstellar medium?
A) The densest interstellar clouds contain from 108-1011 atoms/cm3.
B) The densest interstellar clouds have temperatures as low as 1000 K.
C) Clouds can never resist their own gravity and eventually collapse under its influence to transform into stars.
D) Stars can form in molecular clouds when the densest parts of the clouds become unstable and contract.
Question 2A__________is a stellar object with such low mass that it cannot raise its central temperature high enough to sustain hydrogen fusion.
A) T Tauri star
B) Herbig-Haro object
C) brown dwarf
D) protostar
Question 3A__________is a small, dark cloud only about 1 ly in diameter that contains 10 to 1000 solar masses of gas and dust, thought to be related to star formation.
A) Herbig-Haro object
B) brown dwarf
C) Bok globule
D) T Tauri star
Question 4_____ is the location in the H-R diagram where stars first reach stability as hydrogen-burning stars.
A) The proton-proton chain
B) The carbon-nitrogen-oxygen cycle
C) The zero-age main sequence
D) The interstellar medium region
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