a is an enzyme that adds phosphate groups to other proteins. if this enzyme is only active when bound to a specific protein that fluctuates in concentration in synchrony with the cell cycle, then it is a . please choose the correct answer from the following choices, and then select the submit answer button. answer choices kinase; cyclin-dependent kinase kinase; cyclin-cdk complex cyclin; cyclin-dependent kinase cyclin; cyclin-cdk complex