11.   It is not yet known what caused the crash, police said.

12.   It was not immediately known what caused the blast at the government-run High Energy Materials Research Laboratory.

13.   It was not immediately known what caused the blast at the Kati garrison.

14.   It was not immediately known what caused the rock slide.

15.   It was not known what caused the failure.

16.   It was not immediately known what caused the accident or how many people were traveling on the train.

17.   It was not immediately known what caused the accident.

18.   It was not immediately known what caused the blast.

19.   It was not immediately known what caused the explosion.

20.   It was not known what caused a recent spate of anti-Jewish invective in Yugoslavia.