用括号中所给单词的适当形式填空。

1. Please call me if you have any problems __________ (work) out.

2. Marie Curie received the Nobel Prize __________ (two) during her life time.

3. I think it is __________ (danger) for children to be close to wild animals.

4. The old man has been __________ (die) since three years ago.

5. I know only one of the ___________ (visit), how about you?