21. Why are Tanabe-Sugano diagrams often preferred over Orgel diagrams for interpreting the spectra of d² to d⁸ complexes? (A) Orgel diagrams are only used for d⁰ and d¹⁰ systems. (B) Orgel diagrams do not include spin-allowed transitions. (C) Tanabe-Sugano diagrams are simpler because they ignore electron-electron repulsions. (D) Tanabe-Sugano diagrams treat the Racah parameter B as a variable, allowing for the inclusion of both high-spin and low-spin states. (E) Orgel diagrams are only valid for tetrahedral complexes.