[单选题]
How fast should a moving cl8 ppjj l)ou,p:5+hnr mock travel if it is to be observed s22rjpuo091n0 dmx vl7k fx2rby a stationary observerdsx22j7 o0f0k r9nl up1mv rx2 as running at one-half its normal rate?
A. $0.50 \; c$
B. $0.65 \; c$
C. $0.78 \; c$
D. $0.87 \; c$
