Try process of elimination.
The "following is an assumption..." says that the answer is not actually stated. The other answers should be clearly stated, so first eliminate the ones that are clearly stated. Once you've done that, if you still have multiple answer choices and you're sure you've eliminated everything that is directly stated, you might eliminate anything that absolutely could not be inferred from the passage. These might be things that are directly argued against, for instance. You should now be at 1 answer that is compatible with the passage but not actually stated directly (although it could likely be inferred from the passage or would likely answer the question "which of the following would the author likely agree with?")