根据以下资料，回答17~20题。 THE TOP 10 TIPS TO BEAT TERROR BY MI5(Military Intelligence 5 军情五处) BRITAIN'S security service MI5 issued an unprecedented (前所未有的) warning to firms yesterday to protect themselves from terror attacks．Spy bosses released a list of top 10 tips for companies and their workers saying the cooperation of ordinary people was a vital weapon in the war on terror．MI5 boss Eliza Manningham-Buller said: 'We have a well-developed understanding of international terrorism and other threats facing the UK today.' 'We rely heavily on public assistance and support to do our work effectively．I would encourage people to use our website to pass on any information.' MI5's site warns al-Qaeda (基地组织)is targeting Britain from internally and abroad, and urges the public to report suspicions to a web link or emergency number．British businesses are further advised: 1．Judge the risk of threats and vulnerable points (弱点) 2．Plan security measures for new buildings. 3．Put someone in charge of security awareness, inform. staff and train in emergencies and bomb threats. 4．Keep public areas tidy and well lit, remove unnecessary furniture and cut the shrubs. 5．Search bags and consider a barrier system and car park that keeps unfamiliar vehicles at a distance. 6．Install locks on windows and doors, Closed Circuit TV, alarms and lighting according to circumstances. 7．Consider setting up a mailroom away from your main premises and train staff for a crisis． 8．Follow up staff references. 9．Ensure a reputable and reliable IT (Information Technology) service. 10．Plan how you will function if your premises or IT systems are put out of action by an incident. According to the text, terrorism __. A．is threatening USA B．is threatening Great Britain C．is threatening USA and Great Britain D．is threatening outside Great Britain