Which of the following statements about flame detectors is MOST accurate?

Which of the following statements about flame detectors is MOST accurate?
 
  A. Infrared flame detectors can be designed to be sensitive to only light produced by hostile fires.
  B. Ultraviolet flame detectors are recommended for areas where intense mercury-vapor lamps are used.
  C. Infrared flame detectors are virtually insensitive to sunlight, and can be used in areas not suitable for ultraviolet detectors.
  D. Ultraviolet flame detectors are virtually insensitive to sunlight, and can be used in areas not suitable for infrared detectors.