a ; p < 0.05 in comparison with group 1.   b ; p < 0.05 in comparison with group 2 c ; p < 0.05 in comparison with group 3 d ; p < 0.05 in comparison with group 4 e ; p < 0.001 in comparison with group 1 f ; p < 0.001 in comparison with group 2 g ; p < 0.001 in comparison with group 3 h ; p < 0.001 in comparison with group 4