HI abhasjha,

This is a really quirky SC; it's built on a few Style/Idiom rules and not much else. Most of the incorrect answers are written in a way that "sounds like how people talk." Rather than use individual rules to eliminate a couple of answers at a time, I had to look at all of the rules all at once to select the correct answer.

1) Idiom phrases: The phrases "...pose a threat to....." and "proof that" are what is needed in the context of this sentence. The tricky part about these phrases is that you might use these words in conversation in a different way. They actually combine with another general style rule on the GMAT.....

2) Active Voice: The correct answer to most SC questions uses the Active Voice (the noun comes "before" the verb). Since the noun that "poses a threat" is the "electromagnet fields", it's very likely that the noun ("electromagnetic fields") will come before the verb ("pose any threat").

The only answer that matches all of these rules is C.

For the record, the GMAT doesn't present that many SC prompts in this fashion. You might see 1-2 SCs on Test Day that are just based on "style/idiom/usage" rules, but seeing a prompt that offers nothing else to work with (verbs, pronouns, parallelism, etc.) is rare.

GMAT assassins aren't born, they're made,
Rich