[单选题]
The diagram shows the domy- fap2d caoc cq*8k6,2jxnz6in* 6s/qkb/uw(kab*mo gant cyclin/CDK complexes at different time points in the cell cycle. Which cyclin/CDK complex activates DNA replica*k6b gqkm*u w/sao(/ btion machinery?
A. Cyclin A/CDK 2
B. Cyclin B/CDK 1
C. Cyclin D/CDK 4
D. Cyclin A/CDK 1