**Core Concept**
Criminal abortion, also known as backstreet or black-market abortion, often involves unsafe and unsterile procedures, leading to severe complications. The primary concern is the risk of infection due to contaminated equipment and unsanitary conditions.

**Why the Correct Answer is Right**
Sepsis is the most common cause of death in criminal abortion due to the high risk of infection. This is because the procedure is often performed without proper sterilization, and the equipment used may be contaminated with bacteria. The introduction of bacteria into the uterus can lead to a severe infection, which can rapidly progress to sepsis. Sepsis is a life-threatening condition that occurs when the body's response to an infection becomes uncontrolled and causes widespread inflammation. In the context of criminal abortion, sepsis can be particularly deadly due to the high risk of infection and the potential for delayed medical attention.

**Why Each Wrong Option is Incorrect**
**Option A:** Hemorrhage is a potential complication of abortion, but it is not the most common cause of death in criminal abortion. While hemorrhage can be severe and life-threatening, sepsis is a more common and deadly complication in this context.
**Option C:** Air embolism is a rare but serious complication of abortion, particularly if the procedure involves the use of vacuum aspiration or other equipment that can introduce air into the uterus. However, it is not the most common cause of death in criminal abortion.
**Option D:** Perforation of the uterus is a possible complication of abortion, but it is not the most common cause of death in criminal abortion. While perforation can be severe and may require surgical intervention, sepsis is a more common and deadly complication in this context.

**Clinical Pearl / High-Yield Fact**
In the context of abortion, the risk of infection and sepsis is increased when the procedure is performed without proper sterilization and equipment. This highlights the importance of safe and sterile medical practices in preventing complications and ensuring patient safety.

✓ Correct Answer: B. Sepsis