I want to test the ability of students to read a passage and answer questions about it. Could you please come up with a good question for the passage "There are also open compression formats like Opus and Vorbis that are available free of charge and without any known patent restrictions. Some of the newer audio compression formats, such as AAC, WMA Pro and Vorbis, are free of some limitations inherent to the MP3 format that cannot be overcome by any MP3 encoder."? 

What is the price of Opus?