Understanding the argument -
A theory is either true or false.
Galeleo's observations of Jupiter's satellites showed that the Ptolemaic theory of motion is false.
Ptolemaic theory is inconsistent with Copernican theory.
So, Galeleo's observations of Jupiter's satellites showed the truth of Copernican theory.
Though crystal clear, the argument can be bewildering or confusing if read in a hurry.
So read carefully and connect the sentences. The argument is based on a key assumption: one of the theories has to be true, or both can't be false simultaneously. Because if both are false at the same time, then in this case, we can't say with 100% confidence that falsifying Ptolemaic's theory automatically means that Copernican theory is true.
There could also be another assumption, which is that there can be, say, 20 other theories than Copernican theory and Ptolemaic theory, but as the argument is limited to these two theories, we can ignore this assumption for now.
Option Elimination -
(A) Whoever first observed something inconsistent with the truth of the Ptolemaic theory should be credited with having proved that theory false. - Whosoever gets credit is not even an issue in the argument. Out of scope.
(B) There are some possible observations that would be inconsistent with the account given by the Copernican theory but consistent with the account given by the Ptolemaic theory. Then what? Just use similar words from the argument and arrange them to create some random option. Distortion.
(C) The Ptolemaic and Copernican theories, being inconsistent, cannot both be based on exactly the same evidence. - At best, it is a weakener. It's trying to say that both The Ptolemaic and Copernican theories can't be based on the same evidence. But here, we use the same evidence to establish the truth of Copernican theory and falsify Ptolemaic theory.
(D) Numerous counterexamples were necessary in order to show the Ptolemaic theory to be false. - No. We just used one example as shared in the argument. What happened other than the scope of the argument given is none of our business. Out of scope.
(E) The Ptolemaic and Copernican theories, being inconsistent, cannot both be false. - ok. If we negate this option, it shatters the conclusion.