Answer:
d. They always invade the human body from the external environment
Explanation:
Antigens are the molecules that have the ability to stimulate immune response and are mostly protein in nature. However, an antigen may be self or non-self molecule.
This means that antigen may enter the human body from the external environment (the non-self antigen) or any molecule present inside the body may serve as antigen (self-antigen). Self-antigens are responsible for autoimmune disorders.
Answer: What substances dissolve in ocean water.
This is the only question that can be answered through scientific investigation because it is the only question that can be tested. The other questions cannot be answered through scientific investigation because they based on opinions which are more abstract.
I don't know if this will help you or not but here you go.
https://quizlet.com/225903868/lesson-11-the-nature-of-life-unit-test-biology-a-unit-1-the-nature-of-life-flash-cards/
Similar DNA may support "common" ancestry. ☺