Which of the following statements is TRUE renal tubular functions?

When the Glomerular filtrate enters the renal tubules it flows through the successive pas of the tubule (i.e. the proximal tubule, loop of Henle, distal tubule and finally collecting ducts) before it is excreted as urine. Along its course the tubular cells may selectively secrete some substances from the blood into the tubular lumen (tubular secretion), or may selectively remove some substances (tubular reabsorption) from the tubular filtrate, or may do both. Clearence refers to the viual volume of plasma cleared of a substance in a given time. Clearence is therefore affected by glomerular filtration, tubular reabsorption and tubular secretion. If the clearance for a substance is greater than GFR then there is net tubular secretion of that substance. If the clearance for a substance is less than the GFR then there is net tubular reabsorption of that substance. If the clearance for a substance is same as GFR then there is no tubular secretion or reabsorption of that substance.