Cheers leesunhyeong, welcome to Bike Forums.
Apparently your entire class in Korea is posting their quadcycle designs in Bike Forums, looking for feedback, review and advice. Our Bike Mechanics and General Cycling forums are getting flooded with these.
I'm moving your thread to Manufacturer, Retail, Survey and Consumer Feedback forum (from Bike Mech).
--Juha, a Forum Mod