In the condition diabetes mellitus, why does glucose appear in the urine?

A  Without the hormone insulin, glucose cannot enter proximal tubule epithelial cells.

B  The filtered load of glucose becomes greater than the tubular maximum for its reabsorption.

C  The rate of tubular secretion of glucose becomes greater than the sum of glucose filtration and reabsorption.

D  The plasma concentration of glucose becomes so high that it diffuses from peritubular capillaries into the proximal tubule, down its concentration gradient.

E  Without insulin, the glomerular filtration barrier becomes extremely leaky to glucose, which is not normally filterable.