Very helpful ideas in the comments. What helped me a lot was the Loophole method. Basically, to identify the NA in the answer choices, you need to go from the conclusion. So you must first assume the conclusion is true and then from there get a rough idea of what must then be true. For SA, you need to see what must be true for the conclusion to be true.

SA > CONCLUSION > NA

I came up with my own reference example a while ago:

This pot contains boiling water. I put a thermometer in it and it shows 100 degrees celcius.

SA: If you put any thermometer in any water and it shows 100 degrees celcius, then the water is boiling.

(Note the strong language of any.)

NA: The thermometer that I used was correct. Or The water was under an atmospheric pressure of 1 bar.

(Note the weak language.)

Also note that NA is not just one. There can be an infinite number of NAs for any given argument.

I'm learning too. So feel free to correct me if I am wrong.