In this task, you are given a paragraph, and your task is to construct a question from the given passage. Construct question in such a way that (i) it is well explained in the paragraph, (ii) the words may/may not be present in the paragraph, (iii) it should start with what/how/describe. Avoid creating a question that (i) is just relevant to one or two sentences, and (ii) not relevant to passage. 

Waste builds up in the blood. Blood enters the kidney. Blood passes through nephrons in the kidney. Different kinds of waste are momentarily trapped in the kidney. Cleaned blood flows out of the kidney. Filtered waste accumulates in liquid form (urine). Urine flows out of the kidney into the bladder. 
Describe what kidneys do