with whiCh oF thE Following is thE pAssAgE primArily ConCErnED
A．thE possiBility oF ChAnging thE mArtiAn EnvironmEnt.
B．thE ChAllEngE oF intErplAnEtAry trAvEl.
C．thE ADvAntAgEs oF EstABlishing ColoniEs on mArs.
D．thE nEED to stuDy thE mArtiAn ECology.