21.   Investigators say nuts were missing from a key bolt in the track-switching points at Potters Bar, causing a track to fracture under the added stress.

22.   Investigators say nuts were missing from key bolts in the points structure, causing a track to fracture under the added stress.

a. + stress >>共 364
post-traumatic 18.45%
repetitive 4.90%
emotional 4.23%
psychological 2.72%
great 2.42%
mental 2.12%
financial 2.06%
severe 2.00%
traumatic 1.75%
enormous 1.39%
added 1.33%
added + n. >>共 848
cost 3.87%
pressure 3.58%
bonus 3.03%
benefit 2.88%
security 2.50%
incentive 2.39%
advantage 1.89%
weight 1.86%
burden 1.51%
protection 1.46%
stress 0.64%
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