Red bone marrow, thymus; sites where stem cells become immunocompetent
a. chyle
b. lacteal
c. lymph
d. primary lymphatic organs
e. secondary lymphatic organs

Primary lymphatic organs

Explanation:

Primary lymphoid organ is the site of formation and maturation of lymphocyte. These lymphoid organs provide proper environment for the maturation of immune cells.

The primary lymphoid organ are red bone marrow and thymus. B- cells born and mature in the bone marrow. T cells from the site of origin migrate to the thymus for the maturation.

Thus, the correct answer is option (D).

1. amino acid refers to the fundamental building block of proteins, comprising of an amino group and a carboxyl group.

2. catalyst refers to any substance, which increases the rate of chemical reaction without being used up in the reaction.

3. a complex molecule containing he genetic code is dna or deoxyribonucleic acid.

4. an enzyme refers to a molecule of protein, which is unique in accelerating up a particular chemical reaction in the biological systems.

5. nucleic acid refers to an sequence of sugars, phosphates, and nitrogenous bases, for example, dna and rna.

6. a protein refers to a large, composite organic molecule comprising of a huge number of amino acids associated together with the of peptide bonds.

7. rna refers to a nucleic acid that takes part in the production of proteins.

8. substrate refers to a compound, which takes part in a chemical reaction, and is chemically modified by the reaction.