The four tenants of evolution by natural selection

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

Plsss > .< compare and contrast the characteristics of flatworms rounds worms and earthworms

How can you tell the difference between rough er from smooth er?