张湘怡的回答：

To read such books today主语 is系动词 to marvel at the fact that their learned contents were once deemed suitable for publication in general-circulation dailies动词不定式短语作表语，解释主语. that their learned contents were once deemed suitable for publication in general-circulation dailies同位语从句，解释the fact 今天读到这些书，你会惊讶于这样一个事实: 这些书中渊博的知识曾一度被认为适合在一般发行量的日报上发表。

林中森的回答：

To read such books today主语 is系动词 to marvel at the fact that their learned contents were once deemed suitable for publication in general-circulation dailies动词不定式短语作表语，解释主语. that their learned contents were once deemed suitable for publication in general-circulation dailies同位语从句，解释the fact 今天读到这些书，你会惊讶于这样一个事实: 这些书中渊博的知识曾一度被认为适合在一般发行量的日报上发表。

陈金桥的回答：

To do ... is to do, 这是动词不定式作主语和动词不定式作表语的情况。简单地说两个动词不定式是个相等的关系。如：To see is to believe. 看见就是相信（眼见为实）。

寻梦的回答：

it's said that he has been studying abroad for 3 years.留学三年了证明他可能还在继续留学用现在完成进行时表动作由过去发生延续到现在并可能继续延续下去he is said to have been studying abroad for 3 years