Last Updated: Monday, April 23, 2007 | 4:26 PM ET CBC News In an effort to help save the environment, U.S. singer Sheryl Crow is calling on everyone to limit the amount of toilet paper used "in any one sitting" to one square. Crow made the suggestion in her blog chronicling her recent tour of the United States on a biodiesel-powered bus to raise awareness about climate change. She and environmental activist Laurie David toured 11 university campuses to persuade students to act to help safeguard the world's environment. "I have spent the better part of this tour trying to...