**Core Concept**
Atrial systole is the period during which the atria contract to pump blood into the ventricles. The duration of atrial systole is a critical component of the cardiac cycle and can be influenced by various factors, including heart rate, blood pressure, and autonomic nervous system activity.

**Why the Correct Answer is Right**
The duration of atrial systole is approximately 100-150 milliseconds. This short duration is due to the relatively high pressure in the atria, which allows for rapid contraction and relaxation. The atrial contraction is also influenced by the intrinsic pacemaker cells in the sinoatrial node, which generate electrical impulses that trigger atrial contraction.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the duration of atrial systole is not typically measured in seconds.
**Option B:** This option is incorrect because the duration of ventricular systole, not atrial systole, is typically around 300-400 milliseconds.
**Option C:** This option is incorrect because the duration of diastole, not atrial systole, is typically around 700-1000 milliseconds.

**Clinical Pearl / High-Yield Fact**
Atrial systole is an important component of the cardiac cycle, and its duration can be affected by various clinical conditions, including heart failure, hypertension, and atrial fibrillation.

**Correct Answer: C. 100-150 milliseconds**