**Core Concept**
The question is testing the understanding of the recommended dose of anti-rabies serum for passive immunization in adult victims of dog bites. Passive immunization is a strategy used to provide immediate protection against rabies by administering antibodies to the victim.

**Why the Correct Answer is Right**
The World Health Organization (WHO) recommends a dose of 20 IU/kg body weight of anti-rabies serum for passive immunization in adult victims of dog bites. This dose is based on the assumption that the serum will provide sufficient antibodies to neutralize the virus and prevent the development of clinical rabies. The serum contains antibodies against the rabies virus, which are essential for neutralizing the virus and preventing its spread to the central nervous system.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as the recommended dose is not 10 IU/kg body weight.
**Option B:** This option is incorrect as the recommended dose is not 40 IU/kg body weight.
**Option C:** This option is incorrect as the recommended dose is not 30 IU/kg body weight.

**Clinical Pearl / High-Yield Fact**
It is essential to note that passive immunization should be administered as soon as possible after the bite, ideally within 24-48 hours, to be effective.

**Correct Answer:** D. 20 IU/kg body weight