When a cell has a stalled $DNA$ replication fork,which checkpoint should be predominantly activated?

If the amount of $DNA$ is $2C$,what will it become at the end of the $S-$phase (in $C$)?

Select the correct statements regarding $S$-phase of interphase:
$I.$ Occurs between $G_{1}$ and $G_{2}$ phases.
$II.$ $DNA$ replication begins in the nucleus.
$III.$ Centrioles duplicate in the cytoplasm.
$IV.$ As $DNA$ is doubled,the number of chromosomes also doubles.
The option with correct statements is:

During which phase of the cell cycle does histone protein synthesis occur in a eukaryotic cell?

What is the primary function of Cyclin Dependent Kinases ($CDK$s)?

What does every newly formed cell follow?