How many different elements are in HCO?

The pattern of this wave changes between its beginning and end. what is true about the amplitude and wavelength of the wave when the pattern changes?

Johnny rode his bike to a friend's house 4 blocks down the street in his neighborhood. he immediately rode back home once he realized his friend was not able to play. what was his displacement for the total bike ride? how did you determine this? what could we use as a reference point to determine he was in motion during his bike ride? why can you use it as a reference point

Which would be the most useful source of evidence to support mcneill's contention?