Why are plastics known as synthetic materials?

Using data from seismic waves, geologists have learned that earth’s interior is made up of several

If blood contains 150g of hemoglobin per liter of blood, how much hemoglobin would be contained in 10 ml of blood

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.