During the Initial Visit with the Nurse at the Fertility

During the initial visit with the nurse at the fertility clinic, the patient asks what effect cigarette smoking has on the ability to conceive. The nurse's best response is:

A) "Smoking has no effect."
B) "Only if you smoke more than one pack a day will you experience difficulty."
C) "After your first semen analysis, we will determine whether there will be any difficulty."
D) "Smoking can affect sperm motility."