28. If a reaction suddenly cannot be repeated under your operation, what is your first step?(A) Do other reactions or experiments, so my Professor will forget to ask me about it later(B) Report to my professor, and he/she will tell me what to do next.(C) Make a variable checklist (e.g., temperature, concentrations, solvent, reagent purity, atmosphere, stirring, equipment, and batch-to-batch differences), and then carefully check all the variables one after one until knowing what the problem is.(D) Increase the temperature first to see whether it improves.(E) None of the above