难度加大英文

formal writing would be "The difficulty of the final exam should increase"(正式)more casual would be "the final exam should be harder"（非正式）

With the improvement of students' performance,the examination is becoming more and more difficult compared with the ones several years ago.(注意，“水平”不能译为LEVEL，那样不符合英语表达习惯）

可以用advanced English或者demanding level of English

从词汇上讲就是多用高级词汇，长难词，名词性质的结构代替动词和形容词，能不用动词短语的就用动词替换。从句法上看，各种句什结合，名词性从句，定语从句，强调句，到装句等。从够篇上看，多用连接词，使文章衔接起来更流畅。