Which one of the following statements about mixtures is correct [2] [3] the different substances in a mixture are always in a definite proportion to cacho a mixture is made up of elements that are chemically combined it is extremely difficult to separate a mixture into different substances a mixture must contain at least two different substances a mixture is always homogeneous.

Nebulae are enormous clouds in outer space. they are made mostly of hydrogen gas, helium gas, and dust. some nebulae glow brightly, while others do not. the stars that people see are huge, bright balls of glowing gas. they are made mostly of hydrogen and helium. which statement correctly describes other ways in which nebulae and stars are different? a. stars can form inside a nebula but a nebula can never be produced by any star. b. a star always has a higher density than a nebula. c. stars can never form inside a nebula but a nebula can be produced by any star. d. a nebula always has a higher density than a star.