Here are some ways a question may ask you to figure out which answer must be true given what was said in the passage:
Often there are several things that must be true. You might identify one or two inferences without seeing the one that they have in mind. That’s okay. As you read each answer choice, the only question you need to ask yourself is: “Does this answer have to be true?” The correct answer will be 100% proven by the evidence in the passage.
Engage with the passage and ensure that you understand it. Then make a strong prediction.
Everything in the passage is evidence. The passage will usually be a series of facts. It might also have an argument. Don’t worry about real-world accuracy. Assume everything in the passage is true.
Based on that evidence, predict what else must be true. The best way to do this is to look for links between statements. Can you put them together to make a new inference?
For instance, if the passage says that “most vacations are expensive” and that “anything expensive is worth doing at least once,” you can infer that “most vacations are worth doing at least once.”
If the passage is long and convoluted, compare each answer with only the part of the passage that seems relevant to that answer. Then ask yourself: “Does this answer have to be true given what the passage says right here?”
Don’t ignore the other parts of the passage; just divide and conquer.
If the passage is comprised only of if-then statements, link them in your head. Diagramming on Logical Reasoning is a waste of time that often ends up confusing students more than the passage itself does. Get comfortable with making sense of the passage in your head and making commonsense connections between ideas that share a link.
The correct answer will either (1) restate something that was already said in the passage, or (2) combine two or more facts to make a new inference that is 100% proven by the passage.
Answer choices with weaker wording are generally easier to prove. Strongly worded statements rarely have to be true—unless the passage proves otherwise. In the example above, it’s easier to prove that “most vacations are worth doing at least once” than that “every single vacation is worth doing five or more times.” (Remember content is more important than word strength, so don’t use this technique as a crutch.)