The ear pinna is strengthened by

The ear pinna, also known as the outer ear or auricle, is strengthened by "cartilage." Cartilage is a type of flexible connective tissue that is found in various parts of the body, including the ears, nose, and joints. It is composed of cells called chondrocytes and an extracellular matrix made up of collagen and proteoglycans. The ear pinna is made up of a thin layer of skin that covers a framework of cartilage. This cartilage provides the pinna with its distinctive shape and structure, and allows it to maintain its position and orientation relative to the head. It also helps to protect the ear canal and the delicate structures within the ear from injury. While blood pressure, bone, and turgor pressure are all important for various physiological functions in the body, they are not directly involved in strengthening the ear pinna. Therefore, the correct answer is "cartilage."