A terrorist attack in the city of Jerusalem. That's where we start this midweek addition of CNN STUDENT NEWS. Thanks for watching.Two Palestinian attackers with a variety of weapons entered a synagogue early Tuesday.They killed four Jewish worshippers before police arrived and killed the two attackers.One police officer was injured and later died.This was the deadliest terrorist attack in Jerusalem since 2008. The city is holy to three major world religions: Christianity, Islam and Judaism.And Jerusalem status is a major point of dispute between Israel and Palestinian Arabs.After the attack, Israeli Prime Minister Benjamin Netanyuahu called for national unity against the terroristsand against the Palestinian leaders who he says spread lies about Israel.Palestinian Authority President Mahmoud Abbas denounced the attack. But when you see news like this it's disturbing. Where else could this happen?Here is some perspective from CNN's national security correspondent.I realize we come at you almost every day with a new terrorist threat or an update on an old terrorist threat and I understand how that could be overwhelming.So, I want to talk to you the way I talk to friends and family aboutwhat they should truly be concerned about and what they shouldn't worry about so much, what shouldn't keep them up at night.Consistently, U.S. intelligence officials and counterterror officials tell me that the two main groups to be worried about are AQAP,this is al Qaeda in the Arabian Peninsula, a group that's very skilled and is attempted to get explosive devices onto airplanes.