You can't stop progress?

I feel obliged to point out that isotopic fractionation is not "central" to carbon dating. The key to carbon dating is that radioactive carbon-14 decays to nitrogen-14 with a half life of roughly 5700 years, enabling biological material to be dated by its residual carbon-14 content. That is not isotopic fractionation, it's radioactive decay. Isotopic fractionation would be involved if you observed a difference in the ratio of carbon-12 to carbon-13 in plants versus that same ratio in the air.

Honestly, I'd bet the reason the test designers are using these correct "incorrect" answers is because they know they can't include more appropriate examples of non-testable theories. Specifically: "God created the Earth in 7 days", "God created man in his own image", etc. etc.

Also because what we know about thermodynamics tells us that analogous non-carbon (e.g. silicon) "organic"-molecules are less stable and thus less likely to be the basis for life.

Dead on. It's not like you can just look at a pile of dirt (or ice) and tell whether there's something living in it. And you certainly can't do life detection from orbit unless you have a serious biosphere going, which obviously none of these outer solar system moons have. And the Europa drilling ideas that people like to throw around aren't going to be technically feasible in the time frame of the missions to Mars -- if ever.