听力原文： On the second anniversary of the overthrow of Saddam Hussein, there has been a big demonstration in Baghdad calling for the withdraw of America troops from Iraq. The rally, which was organized by the Shiite cleric Muqtada A1-Sadr, drew tens of thousands of demonstrators to the square, where Saddam Hussein's statue was toppled two years ago. Protesters also said they wanted the former Iraqi leader to be put on trial. 'Our demands are ending the occupation of Iraq immediately and the trial of Saddam Hussein and the release of all the Iraqi prisoners.' The demonstration is to ______.