We're told in the argument, that a nervous system is necessary for experiencing pain, so that is not an assumption (an unstated premise) on which the argument depends.In the passage, we're told that we cannot mistreat plants. The reason why we cannot mistreat plants is because plants do not experience pain.Let's say there were organisms that did not experience pain, but still could be mistreated. (The negation of choice "D") If there were organisms that did not experience plain but still could be mistreated, then it's no longer true that we can not mistreat plants simply because they do not experience pain. (The conclusion of the passage). A plant might be an organism that does not experience pain, but could still be mistreated.In other words, for it to be true that we cannot mistreat plants simply because they do not experience pain, it also must be true that only organisms that experience pain can be mistreated.
This is justify the conclusion, and the correct answer choice should SUFFICIENTLY allow the conclusion to be properly drawn in conncetion with the premises given in the stimulus. The conclusion is, "We cannot in any real sense mistreat plants." You need to justify this conclusion using the premise given. Diagram:Premise 1: Plants do not have nervous system.Plants -> ~NS (Nervous System)Premise 2: Having a nervous system is necessary to experience pain.Pain -> NSConclusion: We cannot in any real sense mistreat plants.Plants -> ~MistreatBased on the premises given and looking at the conclusion, you'll note that there is a "jump." Something is missing and just with the information within the stimulus alone will not allow one to arrive at the conclusion that "Plant cannot be mistreated." Try connecting premise 1 and 2 by using the contrapositive for premise 2:Premise 2 contrapositive: ~NS -> ~PainConnect premise 2 and 1: Plants -> ~NS -> ~PainLooking at answer choice D, it says "Only organisms that can experience pain can be mistreated."D: Mistreat -> PainContrapositive: ~Pain -> ~MistreatConnect this contrapositive to the premise 1 and 2, and you get:Plants -> ~NS -> ~Pain -> ~MistreatOr by transitive property:Plants -> ~Mistreat (OUR CONCLUSION)Note that choice D includes ALL ORGANISM, which is not necessary for us to reach the conclusion, but it is SUFFICIENT for us to reach the conclusion noted in the stimulus. On the side note, other choice like "Only organisms with nervous system can be mistreated" can also work.Choice B is incorrect since it's somewhat of a repeat of premise 2. We needed something to bridge the jump between the premises and conclusion. Hope this helps.