**Core Concept**
The incidence of undescended testis in preterm infants is influenced by the complex interplay of hormonal and genetic factors, particularly the impact of fetal development on testicular descent. The process of testicular descent is primarily driven by the action of anti-Müllerian hormone (AMH) and testosterone, which regulate the migration of the testes through the inguinal canal.

**Why the Correct Answer is Right**
Preterm infants are at an increased risk of undescended testis due to their incomplete development and disruption of the normal hormonal balance necessary for testicular descent. Studies have shown that preterm infants have a higher incidence of undescended testis, which is thought to be related to the premature interruption of the normal hormonal cascade. The exact mechanisms are not fully understood, but it is believed that the premature exposure to androgens and the altered expression of genes involved in testicular descent may contribute to the increased risk.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not provide a clear or accurate estimate of the incidence of undescended testis in preterm infants. Without specific data, it is impossible to determine the validity of this option.
**Option B:** This option is incorrect as it suggests a lower incidence of undescended testis in preterm infants, which contradicts the available evidence. While some studies may report varying rates, the overall consensus is that preterm infants are at an increased risk.
**Option C:** This option is incorrect as it implies a specific numerical value without providing context or evidence to support it. Without further information, it is impossible to determine the accuracy of this option.

**Clinical Pearl / High-Yield Fact**
Preterm infants with undescended testis are at an increased risk of testicular cancer, infertility, and other complications later in life. It is essential for pediatricians and urologists to closely monitor and manage these cases to prevent long-term consequences.

**Correct Answer: C. 5-10%**