[单选题]
How fast should a moul wm3 x/k72h vx3wzk3v01q+ )duzpjpvkdw(n jgurly/((z+ 2fk1nif- ing clock travel if it is to be observed by a stationary observer as running at one-ha / 2fnz+ rwidk((gyfnku-l1j(lf its normal rate?
A. $0.50 \; c$
B. $0.65 \; c$
C. $0.78 \; c$
D. $0.87 \; c$
