I would go for 'c'. The reason being, is that it doesn't do much, and I am also assuming that offshore drilling will not affect underwater sources, which are linked to the ocean.
An experiment or survey must be controlled in order to receive accurate results.
In an experimental group, the independent variable is changed. But in the control group, the independent variable stays the same.
All the deserts are found at 30<span>°N because
</span><span>Hot air from the equator rises, then cools, moisture is lost, and the dry air comes down at 30 degrees north and south</span>