[单选题]
How fast should a moving-0p8xr hk9z2 ;fxsthw clock travel if it is to be observed by a stationar/ o 1s(hifjj j v,pw-*k-wqac 7f6sbo7y observer as runninqkpj1wh67/*ioo-f -jj 7s v sc fb(aw,g at one-half its normal rate?
A. $0.50 \; c$
B. $0.65 \; c$
C. $0.78 \; c$
D. $0.87 \; c$