[单选题]
How fast should a mo:gm(mhmv q .2yd0dbgy 09-rw*rz;eyeving clom bh,/6zkfsv j62km6f kfg:2ock travel if it is to be observed by a stationary obs 6, /2gkmbfj 6f2kzsohv k:6mferver as running at one-half its normal rate?
A. $0.50 \; c$
B. $0.65 \; c$
C. $0.78 \; c$
D. $0.87 \; c$
