In which of the following organs do immature lymphocytes differentiate into antigen-sensitive lymphocytes?

What is the basic principle of vaccination? How do vaccines prevent microbial infections? Name the organism from which hepatitis $B$ vaccine is produced.

Choose the true statements.
$I.$ Innate immunity is accomplished by providing different types of barriers.
$II.$ Acquired immunity is present from birth and is inherited from parents.
$III.$ Sweat,tears,acid in the stomach,and saliva prevent microbial growth.

Which of the following antibodies is primarily produced during the primary immune response?

When an organ is transplanted and is rejected by the body,the lymphocytes responsible for the rejection are produced by:

The yellowish fluid "colostrum" secreted by mammary glands of the mother during the initial days of lactation has abundant antibodies $(IgA)$ to protect the infant. This type of immunity is called: