What does the indicated part in the given figure represent?

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:

$A$ boy happens to put his foot on a rusted nail and the doctor gives him an injection. Most likely,what has the doctor administered?

Small proteins produced by vertebrate cells in response to viral infection,which inhibit further viral multiplication,are known as.............

Interferons are synthesized in response to which of the following?

Which of the following is $NOT$ associated with the bone marrow?