Critical Reasoning

Astronomers have created a mathematical model for
determining whether life exists outside our solar
system. It is based on the assumption that life as we
know it can exist only on a planet such as our own,
and that our sun, which has nine planets circling it,
is the kind of star commonly found throughout the
universe. Hence it is projected that there are billions
of planets with conditions similar to our own. So
astronomers have concluded that it is highly probable,
if not virtually certain, that life exists outside
our solar system. Yet there has never been detected
so much as one planet beyond our solar system.
Hence life exists only on planet Earth.
Which one of the following would most weaken the
above argument?
(A) Thousands of responsible people, people with
reputations in the community to protect, have
claimed to have seen UFOs. Statistically, it is
virtually impossible for this many people to
be mistaken or to be lying.
(B) Recently it has been discovered that Mars has
water, and its equatorial region has temperatures
in the same range as that of northern
Europe. So there may be life on Mars.
(C) Only one percent of the stars in the universe
are like our sun.
(D) The technology needed to detect planets outside
our solar system has not yet been
developed.
(E) Even if all the elements for life as we know it
are present, the probability that life would
spontaneously generate is infinitesimal.