Find the error: Most slugs and snails breathe using a lung which opens through a small hole in the side of its bodies.

Of its bodies

Which opens

Breathe

None of these

The correct phrase should be "of their bodies" because "slugs and snails" are plural.

So the possessive pronoun should also be plural ("their" instead of "its").

The corrected sentence would be:

"Most slugs and snails breathe using a lung which opens through a small hole in the side of their bodies."