[单选题]
The diagram shows the dominant cyclin/CDK complex/qz8j1 zkac4 ie jb:apfjcen w5mc 6 g+;y7nr-5s at different time points in the cell cycle. Which cyc ja+mfc;rpby nc ej5-g7w:56nlin/CDK complex activates DNA replication machinery?
A. Cyclin A/CDK 2
B. Cyclin B/CDK 1
C. Cyclin D/CDK 4
D. Cyclin A/CDK 1