In response to the 1993 bombing , a system of road barriers , checkpoints and surveillance cameras referred to as the `` ring of steel '' has been maintained to control entry points to the City .
ADP NOUN ADP DET NUM NOUN , DET NOUN ADP NOUN NOUN , NOUN CCONJ NOUN NOUN VERB ADP ADP DET `` NOUN ADP NOUN '' AUX AUX VERB PART VERB NOUN NOUN ADP DET PROPN .