Assertion $A$: Acquired immunity is characterized by memory. Reason $R$: The secondary immune response is highly intensified.

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:

Antibodies are synthesized by . . . . . . .

Which cells are responsible for the production of immunoglobulins?

Match the following columns:

Column-$I$	Column-$II$
$(A)$ Primary lymphoid organs	$(i)$ Thymus
$(B)$ $MALT$	$(ii)$ Spleen
$(C)$ Organ located near the heart	$(iii)$ Bone marrow
$(D)$ Bean-shaped organ	$(iv)$ Appendix
	$(v)$ $50\%$ of lymphoid tissue

In the list given below,how many are secondary lymphoid organs?
Thymus,Spleen,Bone marrow,Tonsil,Appendix