The paragraph is followed by an incomplete phrase or sentence which summarizes the main idea of the paragraph. Choose the missing words of the phrase or sentence.

Only this year I witnessed what might have been a fatal accident on the No. 5 highroad. I was motoring up from the town and I came upon the wreckage of two cars on the road. The smash had been caused by a car coming down, which swept round a sharp corner at 100km/h and crashed into a car coming up.
I witnessed a(an)（）