Law School Discussion

Hi,
I'm new to the LSAT as well,  I'll try my best to give my take on the question. When I read the question (B) jumped out because it's necessary for the conclusion to be true. The study did not compare any children not on the diet to see if their behavior changed. That's significant because if there was a change without the diet then the findings wouldn't support the conclusion. Furthermore, it attempts to make a generalization about the whole population of hyperactive children, based on a small unrepresentative sample.

Ok, I'm starting to prep for the LSAT, and just got McGraw-Hill's  2012 6 practice test book.  I have used Kaplan in the past and found it to be easy to follow, but McGraw- Hill just seems a little wonky. For example this question:

"Grass has to be mowed every week during the summer but only about once every month during the winter. This is because during the summer the days are longer and the light from the sun is more intense. Both these factors combine to allow grass to glean more energy from the summer sunlight that reaches its leaves. Plants in general react the same way as grass does during the summer---they grow longer and faster for the same reasons grass does. People just do not realize this because, unlike growing grass that needs to be mowed,  the growth spurts of other plants do not require reciprocal actions."

 Which of the following is assumed by the argument?

(A)  Juniper bushes do not need extra pruning during the summer months.
(B)  Grass grows faster in the Spring than in the Winter.
(C)  Increases in light always lead to increases in plant growth.
(D)  Mowing is a task that is not completely necessary during the winter when grass does not grow.
(E)  If there were no extra hours of sunlight during the Summer, plants would still grow faster because of the sun's extra intensity.
_____________________________ _____________________________ _____________________________ ____________

I chose ( C) which I knew was wrong because of the extreme language "always", but I was running out of time and just filled it in so there wouldn't be a blank. The correct answer is (A) , but I think the question was poorly worded.
 Here's their reasoning: " Since a juniper bush is a plant other than grass, its summer growth spurts do not require any reciprocal human actions." Call me crazy but doesn't " no extra pruning" imply that it needs some pruning, thus reciprocal human action?  This question was just annoying so any insight would be helpful.