Explain ways of controlling cdk2 under normal circumstance

Question

Problem:

Please explain all the answers of these questions:

Question 1: State two ways in which the specificity of CDK2 is controlled under normal circumstances.

Question 2: What would be the consequence(s) for the cell if the genes for INK4 CDKis were deleted?

Question 3: What would be the consequence(s) for the cell if the gene for cyclin E were deleted?

Question 4: Why do familial mutations in the RB gene most often present as retinal tumours?Please explain.