In the united states, most of our energy comes from this non–renewable resource, which has a negative effect on the environment.

coal
nuclear
natural gas
petroleum

What would the difference of spectral lines emitted by hydrogen gas in distant galaxies which is normally found at a wavelength of 21 cm on earth, be observed at 21.1 centimeters?

Which is not a source of noise pollution? a)airplanes b)acid rain c)machines d)cars

Write the correct abbreviation for each metric unit