Which of the following statement is true about the tuberculin test and purified protein derivative (PPD)?

• A. The presence of intradermal skin induration is observed in 6 to 8 hours after being applied
• B. The redness of skin or erythema is also measured while reading the tuberculin test
• C. A positive tuberculin test means that a person was infected with M. tuberculosis in the past and continues to carry the viable organism
• D. A positive PPD test indicates that a person can never be infected with M. tuberculosis