Why is it occasionally necessary to combine an electric furnace and split-system heat pump to heat a home? Question 19 options: a) In homes with poor insulation, a two-part heating system is typically required by local ordinances. b) In some environments, the heat pump kicks on only if the electric furnace is insufficient. c) Some localities have ordinances preventing the use of an electric furnace alone. d) In some localities, low outdoor temperatures necessitate a supplemental heat source