You can view the whole book and listen to all the sound files (by clicking the following links "Yes" under the column "Sound Files") before deciding to buy them or not.
After doing payment, you can get the versions that are printable and without watermarks.
If you cannot read the books on the right after clicking the books' names, you can download the Adobe Reader
The sound files are zipped. If you cannot unzip them, you can go to this web site http://www.quickzip.org/ to install the program to unzip them.