5. Who performed the first experiments that proved the physical
existence of antibodies?
A) Tiselius and Kabat
B) Paul Ehrlich and Jules Bordet
C) Tizzoni and Cattani
D) Von Behring and Kitasato

6. What was the unknown substance present in serum that provided
protection on transfer?
A) Antitoxin
B) Opsonin
C) Immunoglobulin
D) Antigen

7. Who coined the term 'immunoglobulin' for the term antibody?
A) Von Behring and Kitasato
B) Tizzoni and Cattani
C) Paul Ehrlich and Jules Bordet
D) World Health Organization (WHO)

8. How many classes of immunoglobulins are there?
A) Three
B) Four
C) Six
D) Five