Cell cycle is regulated by

Answer: Option D

The cell cycle is regulated by all of the above which are Cyclins, Cyclin-dependent kinase and Inhibitory proteins.
The cell cycle is regulated by many cyclins, cyclin-dependent kinases (CDKs) as well as Inhibitory proteins which are a group of serine/threonine kinases. They form complexes with cyclins to stabilize, activate, and phosphorylate CDKs in specific phases.
These are serine/threonine protein kinases that phosphorylate key substrates to promote DNA synthesis and mitotic progression.