The correct option is D Adrenal gland
The endocrine gland secretes their products (hormones) directly into the bloodstream and not through any duct. There are many examples of the pineal gland, pituitary gland, etc. The adrenal gland is also known as suprarenal glands, which produce many vital hormones. It is an endocrine gland, which is located on the top of each kidney. They produce hormones such as mineralocorticoids, glucocorticoids, etc. Hence, option C is correct.