what will eventually happen to australia small rodent and insect population, as well to the natural predators that live in australia if the cane toad population isn't controlled

The correct answer is option B. The shed is not made of iron or steel.

All the metals present in the environment cannot be attracted to the magnet. The magnet generally attract the iron or the steel. In case, the metal is not iron or steel, the magnet would not attach to it. So, there is a possibility, the shed is not made made up of steel, as the magnet does not get attached to it. That is why, the magnet falls on the ground.

In case, the magnet is not magnetised, it should not pull the nail also, and the size of the nail is not enough to pull the magnet down off the shed.