[单选题]
Two astronauts, of m 33*(wshqpji1 jjpq yagus9)1asses 60 kg and 80 kg, are initially at rest in oz cq.c dn(1h hrm)k7nzpt y/.2uter space. They push each other apart. What is their separation after the lighter astrona2qtd .1(cc mnphhr7z )ky. zn/ut has moved 12 m?
A. $15 \; m$
B. $18 \; m$
C. $21 \; m$
D. $24 \; m$
