Just did this test today.  Scary thing about this RC section was that I had this feeling while doing the section that I was doing so well as I was confident that answers I chose were right.  Well, the answer key told me that was not the case.  "W" "T" "F"

I made up the loss by doing well on games and LRs, but that groupthink passage was a bit of shock.  I do not envy those who actually took this test in June and I respect anyone who got less than four wrong on this section.

If I had said "Posting in this thread will cause you to get the score you want on the Oct LSAT," you could weaken my argument by:

a. Showing that people can get the score they want without posting in this thread.
b. Showing that people who have posted in this thread did not get the score they want.
c. Showing that posting in this thread and getting the score you want are actually both caused by being an obsessive LSAT student.
d. Showing that getting the score you want on the Oct LSAT actually causes you to post in this thread (doesn't apply here).
e. Showing that the data I used to reach this conclusion is flawed.

I choose A.

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 -> NS

Conclusion: We cannot in any real sense mistreat plants.

Plants -> ~Mistreat

Based 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 -> ~Pain

Connect premise 2 and 1: Plants -> ~NS -> ~Pain

Looking at answer choice D, it says "Only organisms that can experience pain can be mistreated."

D:  Mistreat -> Pain

Contrapositive: ~Pain -> ~Mistreat

Connect this contrapositive to the premise 1 and 2, and you get:

Plants -> ~NS -> ~Pain -> ~Mistreat

Or 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.

You did really well to do this by memory.  Yeah I got the causal relation between the two, and yes you're right that the correct answer is A: I just don't get it yet.  I've really not had problems with causal reasoning, but for some reason this one was getting to me, but this is helping a little.

I'm not that genius to solve this problem just by memory; I had to look it up.  However, the answer keys to the copies of PTs I have has some issues, especially the 40+ PTs.  Also, my PTs seem to be mislabeled (again, 40+ PTs).

Back to the question, if all else fails you can always resort to POE.  In this case, it actually works pretty well.

Is this question about bee's vision?  If so, then I believe the answer is A (please double check for me if I'm correct since my answer key is messed up last time I checked).

Main point of the stimulus is that bee's vision did not develop in response to flowers' colors, but it is probably the opposite.  Sorta like cause and effect, but the author believes the cause and effect is actually reversed; flowers' color developed in response to bee's behavior.

Flowers' color --caused -> Bee's Vision  X

Bee's Vision --caused -> Flower's color O

Answer choice A introduces a new information indicating that other insects that have vision VERY SIMILAR to that of bee's and it does not depend on object's color (including flower, perhaps).  This actually aligns with the second cause and effect diagram that I displayed above and as a result, it tends to strengthen the argument made in the stimulus.  In other words, information given in answer choice A makes it less probable that the first cause and effect diagram displayed above is true.

I hope this helps at least a little.