The assembly of a cyclin-dependent kinase complex (cdkcs) begins with association of a cyclin and a cyclin-dependent kinase cdk that is than phosphorylated by a cdk-activating kinase and a cdk-inhibitory kinase and finally becomes active by dephosphorylation by a phosphatase. why cdkcs involve such a complex multi-step activation mechanism?

Cyclin-dependent kinase complex (CDKCs) are important in various cell functions; for example, they play a role in the regulation of the cell cycle, they are involved in the cell transcription, messenger RNA proccesing, and diferrentiation of different cell types. They are so important that a complex activation mechanism is neccesary to avoid cell problems for the accidental activation of CDKCs. This hard activation pathways are also common in other protein complex that are essential in the regulation of the cell, the DNA or RNA proccesing and other delicate functions.

the answer is d. chordata

true, i don't really know what you're asking but from the info you provided im guessing the answer is true.