听力原文： Several hundred people have joined a protest near U. S. President George W. Bush's holiday ranch in Texas to demonstrate against the war in Iraq. The two-week-old protest-organized by Cindy Sheehan, whose son was killed in Iraq last year, is being held to call for the withdrawal of the 138,000 U. S. troops deployed there. Cindy Sheehan's 24-year-old son was killed in Baghdad on April 4, 2004, who is among the 1,829 American troops, including 31 this month, who have died in Iraq since the U. S. -led invasion in March 2003. The president--who is spending a nearly five-week-long working vacation at his Texas ranch--said in a speech Wednesday that the sacrifices of U. S. troops were 'made in a noble cause. 'Bush, who said he sympathizes with Sheehan, has made no indication that he will meet with her. What is the passage mainly about?