This Zen task is fairly easy to recognize, and plays a large part in the whole strand of analyzing argument structure. The answer choice will be an "LSAT speak" version of the [piece] of the stimulus highlighted in the question stem. Like the other tasks for the argument structure strand except for main conclusion, any element of the argument's structure could be a part of the answer.
Zen of 180 clients break down a logical reasoning stimulus into the following parts:
A flat statement that presents the situation and provides the impetus for an argument
Most often, the preface is the first clause of the stimulus--HOWEVER, for [piece] plays [role] stimuli, be very cautious about following this maxim as the arguments purposefully jumble the structural elements
All the facts used to prove the veracity of the conclusion
Typically, the evidence is more specific than the premise and often provides key definitions and limiting language such as "every"
Joins the key pieces of evidence with the conclusion statement
Typically the bridge will be close to the conclusion, and thus can be used to identify the crux of the argument.
Can be as complicated as a conditional dependent clause or as simple as a conjunctive adverb such as "however."
The crux of the argument, what should ultimately be remembered, implemented, or considered
The Zen of 180 pencast explanations are for the two sample PrepTests, from June 2007 and October 1996. The question stem for this task is one of the more complicated in the logical reasoning section, as you must not only identify the task, but pay special attention to the [piece] that the stem is specifically referencing. You should be actively reading the stimulus and marking it with both highlighter and pencil, looking to identify the four structural elements of the stimulus and thus proactively categorizing the relevant [piece].