What is the correct definition of an antigen? Please help

A. a dead pathogen introduced into the body to cause an immune response

B. a substance that sends the immune system into action

C. a protein to keep pathogens from harming the body

D. a white blood cell of the lymphatic system

The environments condition has an affect on the inhabitants true or false

Some plants have reproductive structures that them reproduce using natural forces or animals. how does the reproductive structure shown here ensure the reproductive success of plants?

Which barrier to economic development is shown in the following examples? i. the high rate of hiv infection in underdeveloped nations ii. the use of children as soldiers in uganda’s army in the early 2000s iii. low literacy rates in underdeveloped nations with limited exposure to adequate education a. foreign debt b. political instability c. widespread disease d. low levels of social welfare