[单选题]
How fast should a moving clock travel if ith9d)m,- r5kg y e,nkk0ss*enklxyyz4f. z:1m is to be observed fg(+e f*w/k d; n,if;ymu0jzsby a stationary observer as runny, ( ms0ni kgez*dw f+u;/;ffjing at one-half its normal rate?
A. $0.50 \; c$
B. $0.65 \; c$
C. $0.78 \; c$
D. $0.87 \; c$
