I'd like to challenge myself to learn most subjects in English, because I am as ...
Oh no! You are too pathetic ! And you think education is just simply learning English !?
I would rather referring education as a life-long learning experience. Schools should prepare or equip their students with what it takes to cope with the challenges that they will face in the 21st century.
I'd like to challenge myself to learn most subjects in English, because I am aspired to go to the top universities in Hong Kong, that happens to be taught in English. I've also prepared myself to take up such challenge in the past: (state what you have done to prepare to learn in English).
Besides, your school is good at creating a English language rich environment for students to learn English effectively and joyfully.