any word sounds unnatural?

“Wakaba-mark” is a sticker that ( ? new ) drivers who have just acquired their driver’s licenses have to put on their cars for a ( ? period ) of one year after they get their licenses. The stickers look ( ? like ) young ( ? leaves ) that have just come out. Cars ( ? with ) these stickers on them are usually driven at slow speeds, because ( ? of ) the inexperience of the drivers, and there is a higher ( ? possibility ) that they will cause traffic jams and accidents. That’s ( ? why ) these drivers are required to place “wakaba-mark” stickers on their cars, in order to ( ? attract ) the attention of the other drivers ( ? to ) them.