第一句:
当not only放在句首,连接一个句子时,该句应使用倒装语序;而but also后面的句子仍用陈述语序.所以,这句话应该改为-From the above,not only is some Polite Language known,but also the reason of the differences between China and western is understood.
第二句:
essential的其中一个用法是:it is essential(for sb)to do sth,所以应该为-It is essential to keep these differences in mind and pay attention to them when communicating in foreigners.