Hi all, I am applying to several colleges and attempt to address the admission committee about my low grades with the following essay. Please help me check for problems and give suggestions to improve it. Thank you in advance.

Why low GPA and GRE scores

I highly value research and therefore would trade time and effort to studying for exams in order to focus my research. Undoubtedly, not all research yields good result (but not studying for tests most likely shows the impact right away), however being able to establish knowledge and reach new conclusion is my ultimate objective.

Furthermore, research activities encourage and fuel my other academic studies. Ever since I was introduced to the prestigious value of researching during my co-op in the second half of 2004, all my grades at school have been perfect. In fact, it gave me confidence to ask the professor giving me low grade previously to be my thesis adviser (also because I am interested in his research project). The second half of 2006 has been a very busy time period for my research. It is unfortunate that I also have to take the GRE during this time. While I understand most schools and fellowships require this test, I just cannot concentrate on these tests over my current research projects. The result is quite obvious: my GRE score (which I took only once) was low; however in exchange, my research was very promising and became the base for future work.
You need to start off by saying that your abilities aren't reflected in your GPA, or something to that effect.

Many mechanical problems throughout.
I have changed the structure of the essay as follows. Can you please point out to me where the mechanical problems are ? Even though my studies do not require good English however I am greatly interest in improving my writing.
Thanks,

Research has always been the top priority in all my activities, and in the past I took research to an extreme: I would trade time and effort to studying for exams in order to focus my research. Undoubtedly, not all research yields good result (but not studying for tests most likely shows the impact right away), however being able to establish knowledge and reach new discoveries is my ultimate objective.

However, these experiences have taught me a valuable lesson: that I must balance my love of and dedication to research with the other responsibilities of being a student. I have greatly improved my academic performance in the last several semesters (my GPA has been perfect from 2005). In fact, this also gave me confidence to ask the professor giving me low grade previously to be my thesis adviser.

It is unfortunate that I also have to take the GRE during the second half of 2006 when many of my research projects (including my M.S thesis) reach their peaks. I just seemingly cannot concentrate on these tests over my current research. The result is quite obvious: my GRE score (which I took only once) was low; however in exchange, my research was very promising and became the base for future work.
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You need an introduction. You also need to keep the tone positive so you don't come across as giving yourself excuses (e.g. the GRE bit).