**Core Concept**
The question is testing the understanding of the different stages of sleep and their durations. Non-Rapid Eye Movement (NREM) sleep is characterized by slow wave activity and is divided into three stages, with Stage 3 being the deepest and most restorative stage. The correct answer will be based on the typical distribution of sleep stages during a normal sleep cycle.

**Why the Correct Answer is Right**
The normal sleep cycle lasts around 90-120 minutes and is composed of three stages of NREM sleep and one stage of Rapid Eye Movement (REM) sleep. The majority of NREM sleep is spent in Stage 2, which accounts for approximately 50% of total sleep time. Stage 3 NREM sleep, also known as slow-wave sleep, makes up around 10-15% of total sleep time, while Stage 1 NREM sleep is the lightest stage and accounts for around 5% of total sleep time. The correct answer will be based on the relative proportions of each stage.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Stage 2 NREM sleep is not the shortest stage, but rather the longest stage, accounting for approximately 50% of total sleep time.
**Option B:** This option is incorrect because Stage 1 NREM sleep is the lightest stage and accounts for only around 5% of total sleep time.
**Option C:** This option is incorrect because Stage 3 NREM sleep, also known as slow-wave sleep, makes up around 10-15% of total sleep time, but is not the stage with the longest duration.

**Clinical Pearl / High-Yield Fact**
It's worth noting that the distribution of sleep stages can be affected by factors such as age, sleep disorders, and certain medications. For example, older adults tend to spend more time in Stage 2 NREM sleep and less time in Stage 3 NREM sleep.

**Correct Answer: A. Stage 2 NREM sleep is the longest stage, accounting for approximately 50% of total sleep time.**