> > ×今日から始業式
> > ○今日から新学期
> > ○今日が始業式
> I bacame sick three days ago. ＋ I am still sick now.
> → I have become sick for these three days.
> （私はこの３日間病気になる現象を繰り返し継続しています。）

×　I have become sick for these three days.
○　I have BEEN sick these three days.
○　I have BEEN sick for three days.
(私はこの 3 日間、体調が悪い。)

参考：2003/04/08(火)07時26分56秒