This is any functional structure within the confines of a cell; literally a. Small organ; it usually has a membrane-based structure

The correct answer is cell organelles.

Explanation:

A unique membrane-bound composition, which is found inside the eukaryotic cell's cytoplasm, that is, in plants and animal cells is termed as cell organelle. Some of the examples of cell organelles found within the cells of eukaryotes are endoplasmic reticulum, Golgi complex, mitochondria, chloroplast, etc.  

All these organelles play an essential function for the proper functioning of the cell, like chloroplasts found in plants play an essential role in the process of photosynthesis, and mitochondria both in plants and animals are regarded as the powerhouse of the cell.  

i think it’s c but i might be wrong. if i am let me know! have a good rest of your day as well!