13. If the population decay channels of the excited state decay include three channels, such as fluorescence channel (kF = 109 s¯¹), internal conversion channel (kıc = 1012 s¯¹), and intersystem crossing channel (kIsc = 103 s¯¹), what is the observed fluorescence lifetime TF? (A) 1 psec (B) 1msec (C) 1 nsec (D) 1 µsec