Ans. is 'd' i.e., Pituitary tumor Negative progesterone challenge test - which rules out PCOD - (otherwise too, PCOD is a cause of secondary amenorrhea).When next step was done i.e., estrogen, progesterone combined test - It comes out to be positive i.e., compament I system (uterus, endometrium and outflow tract) is normal if properly stimulated by estrogen which rules out mullerian agenesis and ashermann syndrome.Positive estrogen progesterone combined test means the defect is in the production of estrogen i.e., either ovaries, pituitary or hypothalamus.