Answer:
Cell
Step-by-step explanation:
Hi there!
A cell is the smallest unit of a living thing. However, a cell, much like a person, must have other parts inside of it in order to function (it can't function by itself).
The nucleus, ribosomes, and mitochondria are all structures inside of a cell; they are some of the organelles inside of a cell, which help the cell do specific jobs, a bit like how a machine needs special pieces in order to do certain tasks.
Therefore, a cell is the structure that includes all of the others, since the other structures are organelles that help the cell function, and they are all inside of the cell.
Hope this helps!