关于 I thought 后面跟的时态的语法,

既然是经历了一个过程,那就说明从过去到现在看法发生了一定的转变,从认识模糊或片面到当前的想法,如果你想要表达曾经有过的想法（I thought）,那就需要明确哪些是过去的认识,然后再把现在的认识写出来进行对比；如果你想表达一贯的想法,不仅不要用 I thought 去追述过去,而且用“经历一个过程”去发端行文也是不合适的.
以下提供两种修改方法：
改法一：补充过去的认识.
Actually,my understanding and motivation for learning Civil Engineering has been through some different stages.In the beginning period,(补充过去的认识,如：I though civil engineering was so promising a subject that I could rely on it to make more money than anything else....) （承接上文,转折为现在的认识：However,I think）civil engineering is a promising subject in this day and age.Inasmuch as it covers wide and varied activities and projects,which are essential for economic development and city building.It is known that China is a developing country so that is hungry for a large pool of talent of engineering.
改法二：重复过去的认识依旧是现在的看法,但增加了进一步的认识：
Actually,my understanding and motivation for learning Civil Engineering has been through some different stages.In the beginning period,(用过去时态追述过去的认识)I though,civil engineering was a promising subject in this day and age.Inasmuch as it covered wide and varied activities and projects,which were essential for economic development and city building.（从此处承接上文并补充现在的认识：And now I realize that it is not only promising but also important.）It is known that China is a developing country so that is hungry for a large pool of talent of engineering.
总而言之,要说明“过程”,必须要进新旧对比.