Hoàn thành câu với dạng đúng của các động từ sau

Hoàn thành câu với dạng đúng của các động từ sau:
   challenge      discover        depend          investigate         contribute
   cover             conserve       entrap           maintain             mystery 
1. Scientists have made many important new...............of the depth by using modern devices.
2. Community police have made a very positive...................to crime prevention.
3. Destruction of the environment is one of the most serious...................we face.
4. They are investigating the......................disappearance of a young woman.
5. Seventy-five percent of the earth surface is....................by water.
6. The power station has been shut dơn for essential.....................
7. The.....................of the seabed is being carried out.
8. Sperm whale populations are at risk due to hunting and their accidental..................in fishing nets.
9. By the age of eighteen he was completely...................of his parents.
10. The government has just set up a wildlife.....................project.