有些情况下，免费有声读物是由一些志愿者自己录制的，质量虽不如商业性作品好，但书目很多，而且完全免费。
In some cases, volunteers do the audio so the quality of reading may be less than in commercial works, but the catalogs are broad and the price is right-free.
与上述多数矢量格式不同，SVG是完全免费的，没有任何版权或专利权限制，而且其规范完全有文档记录。
Unlike most of the vector formats mentioned above, SVG is free of any patent or copyright restrictions, and its specification is fully documented.
另外一个也许更重要的因素就是当一个产品完全免费的时候，消费者的期望会降低而且更耐心。
Another perhaps even more important factor is that when a product is completely free, consumer expectations are low and consumer patience is high.
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