**Core Concept**
Sellick's maneuver, also known as cricoid pressure, is a technique used during endotracheal intubation to prevent gastric aspiration by occluding the esophagus. This maneuver involves applying pressure to the cricoid cartilage in the neck, which compresses the esophagus and prevents gastric contents from entering the trachea.

**Why the Correct Answer is Right**
The application of cricoid pressure during intubation is thought to prevent gastric aspiration by mechanically compressing the esophagus and preventing the movement of gastric contents into the thoracic cavity. This is particularly important in patients who are at risk of aspiration, such as those with a full stomach or who have a history of gastroesophageal reflux disease (GERD). The cricoid cartilage is a ring-shaped structure that surrounds the esophagus, and applying pressure to this area effectively occludes the esophagus and prevents aspiration.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Sellick's maneuver is not used to prevent hypotension during induction of anesthesia. While cricoid pressure may have some effect on blood pressure, its primary purpose is to prevent gastric aspiration.
**Option B:** This option is incorrect because Sellick's maneuver is not used to improve the visualization of the larynx during intubation. While cricoid pressure may help to stabilize the larynx, its primary purpose is to prevent gastric aspiration.
**Option C:** This option is incorrect because Sellick's maneuver is not used to prevent the movement of the vocal cords during intubation. While cricoid pressure may have some effect on the movement of the vocal cords, its primary purpose is to prevent gastric aspiration.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the effectiveness of Sellick's maneuver in preventing gastric aspiration is still a topic of debate, and some studies have questioned its effectiveness. However, it remains a widely used technique in clinical practice.

**Correct Answer:** D. To prevent gastric aspiration during endotracheal intubation.