Which are valid ways to make an ammonia/ammonium buffer for use in the laboratory? Select one or more: a. Mix some volume of 1 M NH3 with half as much 1 M HCl. b. Mix equal volumes of 1 M NH3 and 0.01 M NH4+. c. Mix equal volumes of 1 M NH3 and 1 M HCl. d. Mix equal volumes of 1 M NH3 and 1 M NH4+. g