Question

A cell must use energy to transport substances
using

Answer 1

Other types are different types of diffusion, which goes down its concentration gradient (it's a spontaenous process and does not need energy - you do no need to force it to go down its concentration gradient).

But endocytosis is a process that the cellular membrane pinches the extracellular fluid and engulfs it.
This requires energy because you need to phsyically move the cellular membrane, against its will. It wants to be in a stable form, but you are forcing it to move a certain way to surround a portion of the extracellular environment and engulf it.

Answer 2

energy

Answer 3

yes