There was a _______look on his face when he met with the______problem. 

___ by thick bamboo and high forest, the ancient city hadn’t been discovered until the 1990s.

Rare species in the world, ______ by hundreds every year, must be jointly preserved by all countries, or humans will encounter ecological disaster in the near future.

The boy insisted ______ in a nearby school. 

 They were walking around the town       a place for the party.