Answer:
The correct answer is a. To remove substances in the blood and place them into the filtrate.
Step-by-step explanation:
Tubular secretion is the removal of wasteful and undesirable substance like drugs , hydrogen ions, urea through urine by active or passive transport.
Substance are added from blood and are transferred to distilled convoluted tubules(DCT) by the help of peritubular capillaries from where they reach to collecting duct and comes out through urine.
So tubular secretion is important to remove wasteful substances from the blood and maintaining the buffering nature of blood by excreting excess hydrogen and potassium ions.