One possible version:

Dear Mum and Dad,

     How are you doing?

     I am writing to you about my feelings of being 18, my gratitude for you and my future plan. Dear mum

and dad, I am already 18 years old, which shows that I have grown up. Now I have learnt much about lire

and become more independent, meanwhile I know in future I will have more responsibilities and face more

difficulties, which I will have to learn to solve it myself.

     Whenever I am thinking of this, I can't help feeling grateful to you. It is you who first give me

encouragement when I meet with difficulties, especially when I am not getting along well with my studies.

Indeed, your inspiration seems to be a lamp, which offers me light of hope, courage and confidence. And

more importantly, you are always teaching me to be good to others, and try to contribute to our society.

     Dear mum and dad, I am now a senior three student, who is racing the national college entrance

examination. First of all, I ought to try my best to pass the exams. I am sure that though my great efforts 

I will be able to realize my dream of being a key university student. Then I Will develop and prepare myself

to be a youth with a strong sense of responsibility and strive to be independent and competitive. Believe in

me, Mum and Dad, I will make a difference.

     Best regards to you.

                                                                                                                                Yours sincerely,

                                                                                                                                 Li Hua