vi.

1. 發生
   Earthquakes occur frequently in this area.

   這一地區經常發生地震。

2. 出現；存在；被發現[Q]
   Do giraffes occur in Africa only?

   長頸鹿是不是只在非洲才有？

3. 被想起，被想到，浮現[（+to）]
   It occurred to me to visit my teacher.

   我想到要去看看我的老師。

   It never occurred to me that he might be in trouble.

   我怎麼也沒有想到他會遇上麻煩。

   A brilliant idea occurred to me.

   我想到一個極好的主意。

   It didn't occur to him that she would refuse his invitation.

   他沒有想到她會拒絕他的邀請。

v.

1. happen; take place.
2. exist or be found to be present in a place or under a particular set of conditions:
   radon occurs naturally in granite.
3. (occur to) come into the mind of.