1, scientists say forests are being destroyed by air pollution
--> scientists blame AIR POLLUTION FOR THE DESTRUCTION OF (THE) FORESTS.

7, you must concentrate on your work more
--> you must apply YOURSELF TO YOUR WORK MORE.

8, It's believed that a general election will be held in Germany
-->A general election ~> 8->

9, although he was very tired, he agreed to play tennis
--> Tired as he was, he ..