资料题：Why did the girl wedge the trough between the doors（  ）。

The girl moved shakily towards the open doors of the lift but before she could step out, the doors shut in her face.The metal cage moved again, this time upwards.Her pursuer had called it from above.He must have been standing with his thumb on the button and now, locked in her small metal trap, she was being hurtled (猛掷)straight back to the roof.She flew at the controls.She had no idea what they were, and in any case, all the labeling was done in German.But one knob was red and this she pressed desperately.With a sickening sensation and a jar, the lift stopped in mid-night.She jammed her thumb hard on the lower most of the rank of buttons, released the red, and after perhaps two seconds of intolerable pause she felt the lift drop once more.This time she was pressed against the doors, waiting, one hand spread against the metal,ready to push, the other clutching the only movable object in the 1i, a big oblong(长方形的)trough(水槽)for cigarette butts, a foot long by nine inches wide, which bad been standing in the comer underneath the control panel.The doors slid open easily on to darkness.Before they were well apart, she was through them and bad turned to ram the metal trough between them as they slid shut.They closed smoothly on the tough, gripped it, held, and stayed open, nine inches apart.The lift was immobilized (不动)。