Which of the following statemets are $CORRECT$ about eukaryotic cell cycle?
- $CDKs$ can phosphorylate proteins in the absence of cyclins
- $CDKs$ can be inactivated by phosphorylation
- Degradation of cyclins is required for cell cycle progression
- $CDKs$ are not involved in chromosome condensation
- $P$ and $R$ only
- $P$ and $S$ only
- $P, Q$ and $R$ only
- $Q$ and $R$ only