Jack is not very decisive, and he always finds himself in a ________ as if he doesn’t know what he really wants to do．

No one has yet discovered who is responsible for the incident but the police are already collecting ______．

As a result of destroying the forests, a large ________ of desert ________ covered the land.

_________ is a growing world problem, and nowadays the United Nations and its member countries _________hard to deal with it．

Scientists have to work hard to keep ________ with modern discoveries and developments..