The rigth answer is cytoskeleton.
The cytoskeleton of a cell is the organized set of biological polymers that give it the essential of its architectural and mechanical properties. The terminological reference to the "skeleton" of vertebrates is, however, misleading since:
* Most components of the cytoskeleton are renewed by permanent polymerization.
* The cytoskeleton is responsible for most of the cell's movement and feeding, which is more like a set of "muscles".
* The mechanical properties of the cytoskeleton are highly variable depending on the components and situations considered.
* The activity of the cytoskeleton has consequences far beyond purely mechanical roles (movement and structure), for example: the regulation of gene expression, cell differentiation or proliferation.
The cytoskeletons of all eukaryotes are quite similar (although important differences exist between animal and plant cells), whereas those recently discovered in prokaryotes appear to be quite differently organized.