The term 'active immunity' means

Which protein is secreted by animal cells in response to viral infection?

What is an antibody?

What constitutes the immune system and what role does it play in the human body?

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:

$T$-Lymphocytes originate from