A、Milk. B、Sleep. C、Exercise. D、Genes. D对话里男士提到孩子父亲近2米高，说明他认为基因是小孩高的关键，故选D。

M: What would you do if you heard a strange noise in the middle of the night?
W: I’d lie awake a little while, waiting to see if it happened again. And if it did, I would get up and see for myself to decide whether to call 911.
Q: How would you describe the woman?

W: I know why that child grows so tall for his age of four. His mother requires him to drink a cup of milk every night before going to bed.
M: That may not be the reason. Have you ever seen his father who is close to 2 meters tall?
Q: What contributes most to the child’s height according to the man?