A、The attack of Islamist terrorists. B、Indonesia had been on high alert. C、Five Jakarta attackers in Indonesia. D、All attackers

Police in Indonesia have identified four out of five of the Jakarta attackers. Two were previously convicted terrorists. Police named one—Afif Sunakim, seen carrying a gun and a bag during the attacks. He was given a seven-year jail term for attending a terrorist camp.
    All five died in Thursday’s attacks, which left two civilians dead and were claimed by Islamic State (IS). Three arrests were made on Friday but it is unclear if they are connected.
    [4]Security forces battled terrorists for hours in the busy commercial district where the terrorists struck. A Canadian and an Indonesian national died, and at least 20 people were injured. The attack ended when two attackers died in a suicide bombing, police say, with the other three killed in gun battles.
    Following recent IS threats, the country, which had been attacked by Islamist terrorists several times in the past, had been on high alert.
3. What is the news report mainly about?
4. What do we learn about the attack from the news report?