How do scientists know that dark matter and dark energy exist even if we can not see them

Dark matter has been given this name because it doesn't seem to interact with regular matter in any way. It doesn't collide with it, or absorb energy from it. We can't see it or detect it with any of our instruments. We only know it's there because we can see the effect of its gravity.

yup! you are correct it is b.

ba geologist finds four sedimentary rock she determines that no geologic events have shifted the layers she labeles them a,b,c,dbfrom top to bottom