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
CO2 in air is measured by 
Select and explain. 
A. Kieffer test, B. EPKJMAN'S test, C. Silvered thermometer, D. Orthotoludene test
A: Kieffer test
Answer: A: Kieffer test 
Explanation: None