Definition: In this task, you will be presented with a passage and have to answer a question based on your understanding of the events inferred from the passage. Try to find the best answer that is most likely to fill in "_". Note that the URLs in the text have been replaced with [Link].
Input: Iraqi warplanes and artillery began pounding Tikrit this morning as 30,000 troops and irregulars prepared to attack the city, a stronghold of the Islamic State insurgency. The operation in the birthplace of former dictator Saddam Hussein was announced last night by Iraq's prime minister, who urged soldiers and government-backed Shiite militias to spare civilians. Speaking from Samarra, the other main city in Salaheddin province, Haider al-Abadi appeared to be addressing fears of reprisals against the Tikrit area's mainly Sunni population. Scroll down for video Attack: Volunteer Shiite fighters, who are supporting the Iraqi government forces in the fight against the Islamic State group fire a howitzer artillery canon in the village of Awaynat near the city of TikritArtillery and warplanes began pounding Tikrit this morning ahead of attackThe city north of Baghdad is a stronghold of the Islamic State insurgencyIraqi Prime Minister Haider al-Abadi calls on troops to spare civiliansTikrit was the scene of a massacre of mainly Shiite army recruits last year 
 Question:The arrival of many thousands of Shiite fighters in the mainly _ city of Tikrit risks inflaming sectarian divisions.

Sunni