Which statement most accurately describes Glomerular filtration rate?

A. A loop-of-Henle mechanism that establishes the medullary osmotic gradient for urine concentration. B. The volume of plasma filtered by all functioning glomeruli per unit time. C. A renal hormone that stimulates red-cell production in bone marrow during hypoxia. D. Release of a mature oocyte from the dominant follicle after the mid-cycle luteinising hormone surge.