In 2019, the United Nations assembled a team of scientists to conduct the biggest ever study of what?

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

Idon’t know the answer and i’ve been stuck on it for a while now skskskskks

Lumps of iron and manganese ore called can be harvested from the seafloor near underwater volcanoes.