Which one is the correct spelling?

1.A '$pioneer^{\prime} is a/an :$

2.According to some studies, dolphins, whales and ¾ other sea creatures use highly sophisticated navigation systems.

3.We have to do some research in order to ¾ the possible factors that could affect the outcome of the project.

4.Many people who live near nuclear plants are concerned. __ go wrong, the impact on the surrounding area could be disastrous.

5.Supposedly, digital versatile disks, or DVD as they are called, are __ resistant \to scratching __ records.

6.The government __ that the projects __ with great success.

7.These differences between the two photographs __ with the help of computer programs.

8.The skill of safe driving __ necessary $\to avoid$ collisions, which __ many thousands of people annually.

9.Salma could not tell __ books were \left on the table.

10.They like \to keep their old houses rather than build new ones __ it is very difficult and expensive \to maintain them.

11.Hydrogen peroxide __ as a bleaching agent because it effectively whitens a variety of fibres and surfaces.

12.__ can be grown on arid land.