What is the main cause of photosynthesis

Which statement correctly describes other ways in which nebulae and stars are different? a. a star always has a higher density than a nebula. b. stars can form inside a nebula but a nebula can never be produced by any star. 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. reset submit

In general, characteristics that an organism survive and reproduce become more common in a population over time. what mechanism of evolution cause this change?

Which of these is not an obstical to the future of space exploration? fundingresearch ideas technologytime