The correct option is D
A. Corpus luteum is formed in ovary after ovulation and degenerates in absence of pregnancy but if pregnancy occurs it persists and secretes progesterone and oestrogen hormones. During pregnancy, corpus luteum also secretes relaxin hormone which dilates the cervix and aids in childbirth.
B. Pituitary gland is the master gland that regulates the activity of other endocrine glands and secretes many hormones like growth hormone, follicle stimulating hormone, thyroid stimulating hormone etc.
C. Pineal gland is a small, rounded and reddish brown gland present at the dorsal side of forebrain. This gland secretes melatonin and serotonin hormones.
D. Ovary is the primary sex organ in females which produce female gametes or ova and some hormones like oestrogen and progesterone.
So, the correct answer is 'Corpus luteum'.