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

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.