[单选题]
The diagram shows the dominlqq: 0zut 2 c:9qzltd(y0 ; 6mlk 6fielbzl1j-yxq/w5ant cyclin/CDK complexes at different time points in the cell cyclmkblw/5l q6e-;yjy06i1lf xze. Which cyclin/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