This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Fluid and Electrolyte Treatment of Specific Disorders, Subject name: Pediatrics
What is the name of this test to be done before drawing an arterial blood gas sample: 
Select and explain. 
A. Virchow test, B. Water hammer test, C. Allen test, D. Trendelenburg test
C: Allen test
Answer: C: Allen test 
Explanation: c. Allen testA - Both radial & ulnar artery are occluded;B - Ulnar artery kept occluded, Radial artery released; These are steps of Allen's test