Lily,  in general,   read as much non-fiction  in English as you can.

  Try to do some general reading in Science. I can offer you some of my own essays for practice if you would like.  They will assist with your vocabulary development.

I don't know indeed,but i 'd like to encourage u

Uncle google will help you.

I send you address website

http://en.wikipedia.org/wiki/Graduate_Record_Examinations

https://www.google.pl/search?q=exam+GRE&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:pl:official&client=firefox-a&channel=nts&gfe_rd=cr&ei=ZMYGVMTgNcaH8QeSwYDwBg

Of course ，I appreciate so much for your help ! My e-mail address is " [email protected]", can you send your essays to me please?