This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
Feature of slow filter (w.r.t. fast filter) is/are : a) Occupies less spaceb) Highly skilled operationc) Poor bacterial qualityd) Takes more time for purificatione) Size of sand is smaller 
Select and explain. 
A. de, B. bc, C. cd, D. bd
A: de
Answer: A: de 
Explanation: Slow sand filter occupies large area (more space).
Slow and filter requires less skilled operation.
Slow sand filter removes more bacteria and has better bacterial control (99.9-99.99%)
Slow sand filter requires longer duration for purification.
Size of sand is smaller (0.2-0.3 mm).