[单选题]
The diagram shows the do.bp6 srzg5.nimi:e+wdt-7 nhiy65y3zs0 xirminant cyclin/CDK complejd 2ljsnrn3/ 3xes at different time points in the cell cycle. Which cyclin/CDK comn 2/sj3r3nldjplex activates DNA replication machinery?
A. Cyclin A/CDK 2
B. Cyclin B/CDK 1
C. Cyclin D/CDK 4
D. Cyclin A/CDK 1