有几个英语句子不懂.the gate that guard the entrances to the professio

/> so that they may unlock the doors of knowledge,the gate that guard the entrances to the professions,to science,art,literature,agriculture---every department of human endeavor.guard前面的that引导定语从句,意思是：通向各个人类文明（human endeavor)各个领域的大门,包括各种职业：科学,艺术,文学,农业等. 

Even the most industrious person might adopt it with advantage to serve as a reminder that,if one allows his faculties to rest,like the iron in the unused key,they will soon show signs of rust and,ultimately,cannot do the work required of them.if前面的that是同位语从句,后面的状语从句（if.key,they...them)是对reminder的解释说明.甚至最为勤勉的人也以此作为警示：如果一个人有才能而不用,就像废弃钥匙上的铁一样,这些才能就会很快生锈,并最终无法完成安排给自己的工作.

 Just as truly as eternal vigilance is the price of liberty,so is eternal industry the priceof noble and enduring success.  so is eternal industry.这个是倒装句啊.记得初中还是高中学的吗?so do I 意为：我也是.同理,so is eternal industry the price of noble and enduring success.正常语序为,eternal industry the price of noble and enduring success（前面么长都是主语） is so. 整句意为：正如.,勤勉将促成巨大的成功 道理也是如此