What is the central idea of the speech?
A.Humans have not discovered proof of alien life because aliens destroyed their home planet trying to find new planets to inhabit.
B.Because living on Mars will be impossible, the search to discover a planet that can support human life is very important.
C.While exploring the possibility of living on other planets is important, preserving Earth should also be a priority.
D.Mars should be humans' first, not second, choice as a home because Earth will be uninhabitable within fifty years.


LET'S NOT USE MARS AS A BACKUP PLANET
by Lucianne Walkowicz