关于你前面自己些的,有一些错误给你说下吧.已经帮你改正了
As a mainland student,I am really attracted attracted by HKU(原因：主语是I,所以主句用HKU就不对了) Meanwhile,at the approach of entering HKU,I find the further steps I take towards her,the tighter I get attached to her.The rich history,extraordinary teaching capacity and international learning atmosphere allow me to learn functional skills and perfect myself.
下面这段是你即将做的吧,所以时态应该用一般将来时
I will choose Business and Economics as my first will because the study of economics provides explanations and predictions,as well as more universal theories,which can help me explain human behavior,and offer insight into the validity of the various political choices competing for our favor.
I was absent from high school for almost a year.And the experience make who I am today.Mathematical competition gave me quick thinking.Debate competition made my expression wiser .Being a monitor made me more careful and responsible.And the pain from the car accident makes me strong and brave.All of these give me a persevering heart,which I will follow after and keep moving forward to HKU bravely.I do hope I could have the opportunity to study in HKU.Thanks you for your valuable patience and time.