Which is the first line of defense in the human body?

Which of the following is a pentameric immunoglobulin and is produced first in a primary response to an antigen?

Which of the following is true regarding $T$-lymphocytes in mammals?

Injection of an antidote against snake-bite is an example of

Which of the following types of immunity is $Non-specific$?

Given below are two statements:
Statement $I$: Bone marrow is the main lymphoid organ where all blood cells including lymphocytes are produced.
Statement $II$: Both bone marrow and thymus provide micro-environments for the development and maturation of $T$-lymphocytes.
In the light of the above statements,choose the most appropriate answer from the options given below: