This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Surgery
Incidence of undescended testis in preterm infants is: 
Select and explain. 
A. <5%, B. 10%, C. 20%, D. 30%
D: 30%
Answer: D: 30% 
Explanation: The incidence of undescended testes is approximately 30% in preterm infants. Remember that undescended testis is more common in preterm when compared with term babies. Ref: Schwaz's principle of surgery 9th edition, chapter 39.