Free technical support is often available in the form of mailing list or newsgroup discussions; nevertheless some background research, knowledge or experience is often required.
The free copy of a book can be custom edited by the publishers to reflect your own previous reading background.
一本书的免费拷贝可以被出版商定制以反映你过往的阅读背景。
3
Background cosmic radiation levels in free space are ten times greater than the maximum acceptable levels for individuals who work in radiation environments on Earth.