Pitcher problems

Simple: "You are at the side of a river. You have a three-litre pitcher and a seven-litre pitcher. The pitchers do not have markings to allow measuring smaller quantities. You need four liters of water. How can you measure four liters?"

Simple: "You are at the side of a river. You have a two-litre pitcher, a five-litre pitcher, and a ten-litre pitcher. The pitchers do not have markings to allow measuring smaller quantities. You need one litre of water. How can you measure one litre?"

Medium: "You are at the side of a river. You have a three-litre pitcher and a seven-litre pitcher. The pitchers do not have markings to allow measuring smaller quantities. You need two liters of water. How can you measure two liters?"