theory is either true

[sogmat]

A theory is either true or false. Galileo’s observations of Jupiter’s satellites showed that the Ptolemaic theory of the motion of celestial bodies is false. Therefore, since the Copernican theory of planetary motion is inconsistent with the Ptolemaic account, Galileo’s observations of Jupiter’s satellites proved the truth of the Copernican theory.
The argument above is open to the objection that it makes the questionable assumption that
A. whoever first observed something inconsistent with the truth of the Ptolemaic theory should be credited with having proved that theory false
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
C. the Ptolemaic and Copernican theories, being inconsistent, cannot both be based on exactly the same evidence
D. numerous counterexamples were necessary in order to show the Ptolemaic theory To be false
E. the Ptolemaic and Copernican theories, being inconsistent, cannot both be false

OA ([E][/spoiler]

[BTGmoderatorLU]

I don't understand it. Can any explain this please.

[EconomistGMATTutor]

The conclusion: Galileo's observations of Jupiter's satellites proved the truth of the Copernican theory.

The evidence: 1) A theory is either true or false.
2) Galileo's observations of Jupiter's satellites showed that the Ptolemaic theory of the motion of celestial bodies is false.
3) the Copernican theory of planetary motion is inconsistent with the Ptolemaic account.

We know that Ptolemy was wrong. We know that Copernicus is inconsistent with Ptolemy. That doesn't mean that Copernicus was correct.
Let's say Dane thinks that 2 + 2 = 5. We know that Sal's opinion is inconsistent with Dane's on this subject. That doesn't mean that Sal is correct. He might think 2 + 2 = 13. Dane and Sal are inconsistent with each other, but they're both wrong. Of course, Sal would be correct if he did know that 2 + 2 =4, but we don't know that. We also don't know what Copernicus thinks, and we can't assume what he thinks. Ptolemy and Copernicus could be inconsistent with each other (which would have been a better way of wording Choice E) and still both be wrong.

Choice A brings in a number of irrelevant pieces of information.
Choice B doesn't add anything new.
Choice C does not need to be assumed. They could have reached different conclusions based on the same evidence.
Choice D is irrelevant background information.

I'm available if you'd like any follow up.