[单选题]
How fast should a moving cloab c4a b:l7/ )i wyaw920wdpws3sd 0o:4 *mt:uiuen3*xgu bujck travel if it is to be observed by a stationary observer as runb: 43ju* e moud* n3uxt0gis:uning at one-half its normal rate?
A. $0.50 \; c$
B. $0.65 \; c$
C. $0.78 \; c$
D. $0.87 \; c$