Which of the Following Statements Is True Concerning Dark-Field Microscopy

Which of the following statements is true concerning dark-field microscopy?

A) This type of microscopy is used in some laboratories to detect spirochetes.
B) The condenser does not allow light to pass directly through the specimen but directs the light to hit the specimen at an oblique angle.
C) This technique involves the alteration of microscopic technique rather than the use of dyes or stains to achieve contrast.
D) All of the above are correct.