An 8 bit ripple counter and an 8 bit synchronous counter are made using flip flops having a propagation delay of 10 ns each. If the worst case delay in the ripple counter and the synchronous counter be R and S respectively, then

A

R = 10ns, S = 80ns

B

R = 40ns, S = 10ns

C

R = 10ns, S = 10ns

D

R = 80ns, S = 10ns