Read the following paragraph first.Erich Honecker, the leader ofEast Germanyat that time, predicted in January 1989 that the Berlin Wall would stand for 50 or 100 more years; however, to almost everyone's surprise, the Wall began to fall in November 9th of that year and was demolished within a few days.According to the indications of the given paragraph, make a right order of the following sentences:①The pressure from the inside of East Germany generated by the nation-wide protest demonstrations in September 1989 was the first driving force behind the fall. ②The last cause was a failure in communication. ③The external pressure, mainly from the Soviet leader Mikhail Gorbachev, also engendered the critical change in East Germany. ④There are three underlying causes that triggered the fall: internal pressure, external pressure and communication failure.