Final answer:
Substance T may be filtered and completely reabsorbed (option X) or neither filtered nor secreted (option W). The possibilities depend on whether the substance is filterable, its molecular size, and its binding status with plasma proteins. Full reabsorption after secretion (option Y) or no kidney entry (option Z) are less likely.
Step-by-step explanation:
If substance T is normally present in the blood but not in the urine, there are a few possibilities concerning its processing by the kidneys. One possibility is that substance T is filtered and then completely reabsorbed back into the bloodstream. This situation would correspond to option X in the student's question. In this case, substance T would initially pass through the glomerulus, a filtration system in the kidneys that removes wastes from blood while retaining components the body can reuse. The substance would then be reabsorbed in parts of the renal tubule such as the proximal convoluted tubule (PCT) or the distal convoluted tubule (DCT). Hence, it would not appear in the urine.
Alternatively, substance T might be neither filtered nor secreted, which would correspond to option W. Substances that are large or bound to plasma proteins are generally not filtered. If substance T does not enter the renal tubule system at all, it could mean that it is a larger molecule or bound to something that prevents it from being filtered.
Option Y, which suggests that substance T is secreted and then completely reabsorbed, seems unlikely since the secretion process is typically reserved for substances the body needs to eliminate. Option Z, which suggests that substance T does not enter the kidney, is possible if it is not part of the substances handled by the kidney but this does not align with the idea of it being filtered or reabsorbed.