6. He ___________(经历) great difficulty in getting a visa to leave the country. 7. Earthquakes, floods, hurricanes and droughts are all natural ________(灾难). 8. That plane crash ________(发生)only minutes after take-off. 9. Tornadoes are ______(强烈的)whirlwinds which vary in their width from a few yards to 1, 300 feet. 10. The police are investigating the _____(原因)of the explosion.

experienced

disasters

occurred

violent

cause