[单选题]
Two astronauts, of ma84d6ixv32 chgj9ot w hildjg q;26 wb1sses 60 kg and 80 kg, are initially at rest in outer space. jb;1lg wd 6iq2They push each other apart. What is their separation after the lighter astronaut has moved 12 m?
A. $15 \; m$
B. $18 \; m$
C. $21 \; m$
D. $24 \; m$
