It is theoretically possible that bacteria developed on Mars early in its history and that some
were carried to Earth by a meteorite. However, strains of bacteria from different planets would
probably have substantial differences in protein structure that would persist over time, and no
two bacterial strains on Earth are different enough to have arisen on different planets. So,
even if bacteria did arrive on Earth from Mars, they must have died out. The argument is
most vulnerable to which of the following criticisms?
A. It fails to establish whether bacteria actually developed on Mars.
B. It fails to establish how likely it is that Martian bacteria were transported to Earth.
C. It fails to consider whether there were means other than meteorites by which Martian bacteria
could have been carried to Earth.
D. It fails to consider whether all bacteria now on Earth could have arisen from transported
Martian bacteria.
E. It fails to consider whether there could have been strains of bacteria that originated on Earth
and later died out.

[spoiler]Why not E?[/spoiler]