**Core Concept**
Ejection fraction (EF) is a critical measure of left ventricular (LV) function, reflecting the percentage of blood that is pumped out of the heart with each beat. It is a key indicator of cardiac performance, with normal values ranging around 55-70% in adults.

**Why the Correct Answer is Right**
The correct answer, **D. 65%**, represents the average ejection fraction in a healthy adult population. This value is determined by the heart's ability to contract and relax, which is influenced by factors such as preload, afterload, and contractility. The ejection fraction is calculated by dividing the stroke volume (SV) by the end-diastolic volume (EDV), and a value of 65% indicates that 65% of the heart's chamber volume is being pumped out with each beat.

**Why Each Wrong Option is Incorrect**
**Option A:** A value of 25% would be considered severely impaired, indicating significant left ventricular dysfunction, which is not normal.
**Option B:** A value of 45% is below the average normal range and may indicate some degree of left ventricular dysfunction.
**Option C:** A value of 55% is at the lower end of the normal range, but still within the normal limits.

**Clinical Pearl / High-Yield Fact**
Remember that a normal ejection fraction is crucial for maintaining cardiac output and ensuring adequate perfusion of vital organs. A reduced ejection fraction can lead to symptoms such as fatigue, shortness of breath, and decreased exercise tolerance.

**✓ Correct Answer: D. 65%**