Use the Following Information as Background for the Next Few

Use the following information as background for the next few questions.
Immunodeficiencies can be genetic in origin,and two examples are Bruton's agammaglobulinemia,an X-linked disorder,and DiGeorge syndrome,caused by a deletion from chromosome 22.Bruton's disorder results in underdeveloped B cells,whereas DiGeorge syndrome results in a missing or seriously underdeveloped thymus.
-Assume that a DiGeorge syndrome-like phenotype was produced in a specific "gene-knockout" mouse,one lacking expression of HA3,a Hox gene known to be involved in developmental regulation in the mouse.
The phenotype of the HA3 knockout can be ascertained by

A) a bone marrow biopsy.
B) an assay for environmental agents known to cause birth defects.
C) a chest X-ray.
D) the measurement of the proportion of CD4 cells to total lymphocytes.
E) an autopsy examination of the adrenal glands.