1. They are working at the scientific problems at present. They aren`t working at the scientific problems at present. Are they working at the scientific problems at present?
2. He was waiting for you yesterday at 3 o'clock. He wasn`t waiting for you yesterday at 3 o'clock. Was he waiting for you yesterday at 3 o'clock?
3. She is translating a german article now. She isn`t translating a german article now. Is she translating a german article now?
4. They were listening to the lecture yesterday at 6 o'clock. They weren`t listening to the lecture yesterday at 6 o'clock. Were they listening to the lecture yesterday at 6 o'clock?
5.He will be preparing for the exam tomorrow all day long. He won`t be preparing for the exam tomorrow all day long. Will he be preparing for the exam tomorrow all day long?
1 count how much water you use a day - посчитайте, сколько воды вы используете в сутки
2 brush teeth - чистить зубы
3 total - очень много значений, но в данном случае, я думаю речь идет об общем количестве чего-то (может быть, воды)