B. Embryologically, thymus is derived from endothelium, and so the stroma does not contain connective tissue.
Overlying epithelium is ciliated, pseudostratified columnar.
Numerous afferent lymphatics empty into the subcapsular sinus. The reticular stroma stains with silver salts. The Hassall's corpuscles are made up of concentrically arranged epithelial cells. D is true. Apparently, the process of immulogical specification is highly prone to errors, which, fortunately for us, are corrected before the faulty T-lymphocytes ever get released.