Background Paragraph: Alberta's electrical demand varies throughout the day and across the seasons. When individuals are fixing supper and using home appliances, demand for power goes up, as it does during heat waves and cold snaps. It tapers off during spring and fall. Like other mechanical devices, generators fail from time to time. If they are wind-powered, their output varies with the wind. 
Story: Alberta has had strange weather this week. On Sunday, there was a cold snap. On Monday, a heat wave happened. On Tuesday, it was normal. On Wednesday, another cold snap happened. On Thursday, a heat wave happened. On Friday, it was normal. On Friday, a cold snap happened in the morning and a heat wave happened at night. On Saturday, a heat wave in the morning and at night. 
Question: What day did demand for power go up: Sunday or Tuesday?
Sunday.