Passive immunity refers to the immunity that is acquired from an external source rather than through the body's own immune response. This type of immunity provides immediate protection against pathogens and their toxins. There are several ways in which passive immunity can be conferred, including through vaccines, antitoxins, and colostrum.

a) Vaccines:
Vaccines are a common method of conferring passive immunity. They contain inactivated or weakened forms of pathogens or their components, such as proteins or polysaccharides. When a vaccine is administered, the immune system recognizes these components as foreign and mounts an immune response. This response leads to the production of antibodies that can recognize and neutralize the pathogen if encountered in the future. By receiving a vaccine, individuals can acquire passive immunity to specific diseases.

b) Antitoxins:
Antitoxins are another way to confer passive immunity. They are derived from the blood plasma of individuals or animals that have been immunized against a specific toxin. Antitoxins contain antibodies that can bind to and neutralize the toxin, preventing it from causing harm in the body. When administered to individuals who have been exposed to or are at risk of a toxin, antitoxins provide immediate protection and help in the treatment of certain infections or poisonings.

c) Colostrum:
Colostrum is the first milk produced by mammals, including humans, immediately after giving birth. It is rich in antibodies, particularly immunoglobulin A (IgA), which can confer passive immunity to the newborn. When a baby consumes colostrum, the antibodies present in it can provide protection against various pathogens until the baby's own immune system develops fully. Colostrum is particularly important for the development of the baby's gut microbiota and the prevention of gastrointestinal infections.

d) Both (b) and (c):
The correct answer is option 'D' because both antitoxins and colostrum can confer passive immunity. Antitoxins provide immediate protection against toxins, while colostrum provides passive immunity to newborns through the transfer of maternal antibodies. Vaccines are not directly involved in conferring passive immunity but rather stimulate the body's own immune response to provide active immunity.