The nephrons have LOHs that span deeply into the medulla. The is the capillary bed that drains these extended LOHs.
a. Cortical; vasa recta
b. Cortical; peritubular
c. Juxtamedullary; peritubular
d. Juxtamedullary; vasa recta

The preferable option for the fill in the blanks will be - D.

D. Juxtamedullary; vasa recta

Explanation:

The juxtamedullary nephrons have LOHs that span deeply into the medulla. The vasa recta are the capillary bed that drains these extended LOHs.

LOH = loop of Henle  

We know that the longitudinal section of the kidney has two regions - 1. an outer dark cortex and 2. inner light medulla. The juxtamedullary nephron is the structural and functional unit of the kidney with a long loop of Henle.  Juxtamedullary nephrons have a long loop of Henle extending deep into the renal medulla. The vasa recta capillaries are long, hairpin-shaped blood vessels that run parallel to the loops of Henle. The hairpin turns slow the rate of blood flow, which helps maintain the osmotic gradient required for water reabsorption.