[单选题]
How fast would a rocketnnc,xg u 4qa w*6u8 f6n.-5dab*kceu b shi sodtn,b8ju m2e.s f.9p have to move to contract to half of its proper length (as observe,one92.b8dujsm t. sf d by a stationary object)?
A. $0.50 \; c$
B. $0.65 \; c$
C. $0.78 \; c$
D. $0.87 \; c$
