I chose [spoiler]A)[/spoiler].

Is [spoiler]A)[/spoiler] the OA?

The reason being:

[spoiler]
P. Theories' testing take for granted other theories.

CA. Therefore, you can retain a theory regardless of the test results if you give up the theory that holds up the incompatible test result.

All others talk about things like initial formulation, which the premise doesn't even discuss.

ANSWER = A
[/spoiler]

I chose A as well, but this is a bit of a challenging problem. I am confused by the wording after the first comma in the statement. I chose A because it talks about relevant information that is given in the statement.

I think the logic here can be exemplified thus:

the argument is saying that you can't test a theory without taking for granted something: at the very least, you assume that your testing instruments work and do their job. For example, you have a theory that the egg you bought at the supermarket is unbreakable. You test it by placing it on the table and hitting it with a hammer, and it promptly breaks. Did you prove your original hypothesis wrong? only if you believe in such weird scientific beliefs as the laws of physics which measure the hardness of the egg shell Vs. the force exerted by the hammer. If you subscribe to this "body of scientific beliefs", then the evidence proves that that the hammer broke the egg, so the egg is not unbreakable.

what A says is that any theory can be proven, provided that you are willing to let go of certain beliefs and not take them from granted. For example, if you do not believe in the laws of physics, then you can argue (against the evidence) that the hammer did not break the egg - the egg is indeed unbreakable, it merely "decided" to spontaneously implode when the hammer came near.

This Q just consumed 10 min of my life and am still bot convinced by the OA.