Final answer:
The normal inactivation of Cdk/cyclin at the G1/S checkpoint requires mitogen-activated G1/S Cdk through binding and phosphorylation.
Step-by-step explanation:
The question is asking about the normal inactivation of Cdk/cyclin in the cell cycle, specifically at the G1/S checkpoint. The mitogen-activated G1/S Cdk is required for the normal inactivation of Cdk/cyclin. For activation, a Cdk must bind to a cyclin protein and then be phosphorylated by another kinase. The binding of the mitogen-activated G1/S Cdk to cyclin and subsequent phosphorylation leads to the inactivation of Cdk/cyclin, allowing the cell cycle to progress forward.