[单选题]
How fast should a moving zlz /c;u6bian;.5ukp clocky)3zfw3 zs1*u1 )ei np6ngwrp travel if it is to be observed by a stationary observer as running at on ze13n1 zun*fi)) ryswp6wpg3e-half its normal rate?
A. $0.50 \; c$
B. $0.65 \; c$
C. $0.78 \; c$
D. $0.87 \; c$
