It could take up to 3 years for a manned spacecraft to reach mars and return to earth. this is a long time for a spacecraft to be supplying cool air and oxygen to the crew and to be processing wastes.

how might manned missions to mars decrease the energy needed to perform these tasks?
a.
put the crew in airtight space suits.

b.
train the crew to live without oxygen.

c.
put the crew in a state of hibernation

d.
train the crew to not produce any waste.