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: Microbiology
The commonest method of detection of diphtheria carriers is: 
Select and explain. 
A. Schick test, B. Dick test, C. Casoni's test, D. Charles' test
A: Schick test
Answer: A: Schick test 
Explanation: Schick test, method for determining susceptibility to diphtheria; it laid the basis for inoculation against the disease. A minute amount of diphtheria toxin is injected into the skin of the forearm. 
Redness at the site of injection after three days indicates a positive reaction (absence of circulating antibody) or a false positive reaction (hypersensitivity to the toxin). 
A positive reaction can be distinguished by use of a control injection of the same amount of heated toxin (toxoid) into the other forearm.