Correct answer is (a) endoderm
Explanation: Endoderm is one of the primary germ layers of embryo. It gives rise to epithelium of pharynx including the eustachian tube, the tonsils, the thyroid gland, parathyroid glands, and thymus gland; the larynx, trachea, and lungs; GIT, the urinary bladder, the vagina, and urethra. Alveoli is derived from the endoderm of the embryo.