Which idea will reduce their energy usage the most, while also reasonable to follow? a) for the time they are home during december, cook meals outside on the charcoal grill instead of inside with the electric stove/oven. b) when they return from their trip, leave the television off for a week, and hang clothes up outside to dry instead of using their electric dryer. c) before leaving for their trip, turn the central heating system off, along with lights and electrical household appliances that will not be in use. d) while they are home in december, they can use candles instead of electric lights, and put their food in coolers so they can unplug their refrigerator.