Which of the following is NOT good direct evidence that the cell-cycle control system is conserved through billions of years of divergent evolution?

A)A yeast cell lacking a Cdk function can use the human Cdk to substitute for its missing Cdk during the cell cycle.
B)The amino acid sequences of cyclins in plants are similar to the amino acid sequences of cyclins in humans.
C)The Cdk proteins in humans share conserved phosphorylation sites with the Cdk proteins in yeast.
D)Yeast cells have only one Cdk, whereas humans have many Cdks.