[单选题]
Two astronauts, of masses 60 kg and 80 kg, are initially at rezqj6qpi79rv4 5eg ms 8stq.t;ip b ,n) mdrhy;5vc.kr2m8g8qw w in outer space. They push each other apart. Whkmrwi) hby.r8.w p2tq5;,8vnm; cdgqat is their separation after the lighter astronaut has moved 12 m?
A. $15 \; m$
B. $18 \; m$
C. $21 \; m$
D. $24 \; m$
