**Core Concept:** Ratio of ventilation to cardiac compression in adult CPR (Cardiopulmonary Resuscitation) with two rescuers is based on the principle of alternating compressions and ventilation to ensure optimal perfusion and oxygenation of the patient's tissues.

**Why the Correct Answer is Right:** In adult CPR, the correct ratio is 30:2, meaning 30 compressions followed by 2 breaths. This ratio ensures that the chest remains adequately decompressed to allow for effective venous return to the heart and adequate oxygenation of the blood. The 30:2 ratio also ensures that each rescuer is performing their assigned tasks efficiently and not getting tired too quickly.

**Why Each Wrong Option is Incorrect:**

A. 15:1 - This is incorrect because it does not allow for adequate venous return and oxygenation of the blood, leading to suboptimal resuscitation outcomes.

B. 20:2 - This is also incorrect as it does not adhere to the 30:2 ratio and may lead to inefficient and fatigued rescuers.

C. 20:1 - This ratio is too long, potentially causing rescuers to tire quickly, leading to suboptimal CPR quality.

D. 15:1 - Similar to option A, this ratio does not ensure adequate venous return and tissue oxygenation, leading to suboptimal resuscitation outcomes.

**Clinical Pearl:** The correct 30:2 ratio ensures optimal perfusion, oxygenation, and rescuer fatigue management during adult CPR, leading to better chances of successful resuscitation outcomes. Always remember the mnemonic "30-2" to ensure proper CPR performance.