This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bacteriology, Subject name: Microbiology
The RPR test uses VDRL antigen containing fine 
Select and explain. 
A. Carbon paicles, B. Iodine paicles, C. Silver ions, D. Sodium ions
A: Carbon paicles
Answer: A: Carbon paicles 
Explanation: The rapid plasma reagin (RPR) test is a macroscopic, nontreponemal flocculation card test used to screen for syphilis. RPR antigen is prepared from a modified VDR antigen suspension containing choline chloride to eliminate the need to heat inactivate serum, ethylenediaminetetraacetic acid (EDTA) to enhance the stability of the suspension, and finely divided charcoal paicles as a visualizing agent. Ref: Ananthanarayana textbook of Microbiology 9th edition Pgno : 374