Energy independence" and its rhetorical (修辞的) companion "energy security" are, however, slippery concepts that are rarely though through.
出自-2014年6月阅读原文
And while he has been doing this, he has been learning other things as well, including many of the concepts that the schools think only they can teach him, and many that are more complicated than the ones they do try to teach him.
出自-2010年6月听力原文