**Core Concept**
The inguinal ligament forms a key anatomical landmark in the lower abdomen, marking the boundary between the abdominal wall and the pelvic region. Structures that pass **behind** this ligament are considered to lie in the **inguinal canal** or deep to the ligament, and their relationship is critical in understanding inguinal hernia formation and surgical anatomy.

**Why the Correct Answer is Right**
- **Femoral branch of genitofemoral nerve (a)** passes behind the inguinal ligament as part of the genitofemoral nerve, which innervates the external genitalia and skin of the anterior thigh.
- **Superficial epigastric artery (b)** runs anteriorly and is a branch of the external iliac artery, but it lies **anterior** to the inguinal ligament, not behind it.
- **Psoas major (c)** is a deep posterior muscle that originates from the lumbar vertebrae and inserts on the femur; it lies **anterior to the inguinal ligament** and does not pass behind it.
- **Femoral vein (d)** runs posterior to the femoral artery and lies **deep to the inguinal ligament** as it passes through the femoral triangle, making it correct.
- **Saphenous vein (e)** is a superficial vein of the leg and does not pass behind the inguinal ligament.

**Why Each Wrong Option is Incorrect**
Option A: The femoral branch of genitofemoral nerve is behind the ligament, but **superficial epigastric artery and psoas major are not**.
Option B: Superficial epigastric artery lies **anterior**, not behind the ligament.
Option C: Psoas major is deep to the pelvis and lies **anterior**, not behind the ligament.
Option D: Only femoral vein and femoral branch of genitofemoral nerve (a), and femoral vein (d) are correctly behind the ligament — thus **acd** is correct.

**Clinical Pearl / High-Yield Fact**
In inguinal hernia repair, the **femoral vein** and **genitofemoral nerve** are important landmarks; the **femoral artery** lies deep to the inguinal ligament, and structures behind it are at risk during surgery.

✓ Correct Answer: D. acd