On Which of the Following Can a Medical Expert on Sexual

On which of the following can a medical expert on sexual disease give his/her opinion? An expert may only give opinion evidence about their field. Like other witnesses, they cannot give general opinion evidence or evidence not in their field of expertise.

A) How A.I.D.S. can affect a defendant's behaviour
B) How the weather affects driving conditions
C) How swine flu can affect a defendant
D) What speed (s) he thinks is a fast running pace