**Explanation:**

The opening to the trachea is covered by a small flap of tissues known as the **epiglottis**. The epiglottis is a leaf-shaped structure made of elastic cartilage located at the base of the tongue, just behind the hyoid bone. It is attached to the entrance of the larynx and acts as a valve to prevent food and liquid from entering the airway during swallowing.

**Functions of the Epiglottis:**

1. **Swallowing:** During swallowing, the epiglottis closes over the larynx, covering the opening to the trachea. This prevents food and liquid from entering the respiratory tract and ensures they are directed towards the esophagus and down into the stomach.

2. **Protecting the Airways:** The epiglottis acts as a protective mechanism for the airway. It closes off the entrance to the trachea, preventing the entry of foreign particles, such as food, liquids, or saliva, into the lungs. This helps to prevent choking and aspiration pneumonia.

3. **Respiratory Functions:** When not involved in swallowing, the epiglottis remains in an upright position, allowing air to freely flow through the larynx and into the trachea. The opening in the larynx, covered by the epiglottis, is called the glottis, through which air passes during breathing.

**Conclusion:**

The epiglottis is a crucial structure in the respiratory system as it helps in swallowing and protecting the airways. It covers the opening to the trachea, preventing the entry of food and liquid into the respiratory tract. The correct answer to the given question is **c) Epiglottis**.

The opening to the trachea is a slitlike structure is called glottis . A thin flap of tissue is called epiglottis.it folds over the opening during swallowing and prevent food from entering the trachea.