If you make use of these cues when you are in doubt about a test, you may increase your chance of obtaining a higher test score. The correct alternative is often the most general, since the most general alternative includes the most information. You will often find a list of items that have some very technical and specific alternatives and one alternative which is more general. Chances are, the most general alternative is the correct one. Even if you aren't sure of the correct answer, you can see that the alternatives A, B, and D, all deal with specific facts and details about the lungs.
C deals with a main feature of the lungs, respiration.
Since C is more general and allows for more variability, it is correct. Length - The correct alternative is often the longest. If you have noticed that most of the correct answers have been the shortest, then when you aren't sure, select the shortest. If, on the other hand, most of the correct answers have been the longest, select the longest answer when you are unsure. In this item, B is the longest and therefore is most likely correct.