How does passive transport compare and contrast with active transport? how does the concentration gradient affect whether transport is passive or active?

If you are going from a high gradient to a low gradient it’s passive transport. Think of a hill if you put a rock at the top of that hill it will go down no energy involved. Active transport is going up the hill you must use energy to push that rock up the hill because it’s from a low gradient to the top. Hope this helps

idk but if i had to take an educated guess i’d say a c d