Salam!
There's nothing better than making the pps listen and practise.
The following, may be useful to confirm and check the pps' assimilation of the prepositions: under, on, in....
You may use them as they are or simply get a new method to check / review these lexical items.
Worksheets
http://www.mediafire.com/?nyakm4gyej4
Audio
]http://www.mediafire.com/?nlyzmj2myk2
You'll find many interesting things through this link
http://www.cambridge.org/elt/elt_projectpage.asp?id=2500124
Wish you'll find them useful!
Salam!