A 24 year old male presents to a STD clinic with a single painless ulcer on external genitalia.The choice of laboratory test to look for the etiological agent would be:

• A. Scrapping from ulcer for culture on chocolate agar with antibiotic supplement
• B. Serology for detection of specific IgM antibodies
• C. Scrapping from ulcer for dark field microscopy
• D. Scrapping from ulcer for tissue culture