What is a checkpoint?

a.) the phase of the cell cycle where the cells check to make sure the DNA has been replicated

b.) when vesicle-mediated protein sorting cargo is loaded into a vesicle, this checks to make sure the cargo is correct

c.) a phase of the cell cycle when the cells stop to rest before cell division

d.) a mechanism that halts cell cycle progression until a critical phase of the cell cycle, like replication, is completed

e.) when a cyclin protein phosphorylates a CDK, the cell cycle can progress