why is the decreased affinity of fetal hemoglobin for bpg advantageous? a) with fewer bpg molecules bound there are more heme residues available for o2 b) decreased bpg binding biases the fetal hemoglobin toward the r state. c) more free bpg is available to bind to adult hemoglobin, resulting in a shift to the r state. d) bpg is available to bind to fetal myoglobin, helping to release o2 in fetal muscle tissue. e) none of the above